Chemical Society Reviews

Recent advances on functionalized micro and mesoporous carbon materials: synthesis and applications

Journal: Chemical Society Reviews

Manuscript ID CS-REV-11-2017-000787.R1

Article Type: Review Article

Date Submitted by the Author: 09-Feb-2018

Complete List of Authors: Benzigar, Mercy; a. Future Industries Institute, University of South Australia, Mawson Lakes 5095, Adelaide, South Australia, Australia, Engineering Talapaneni, Siddulu Naidu; The University of Newcastle, Global Innovative Center for Advanced Nanomaterials (GICAN), Faculty of Natural Built Environment and Engineering Joseph, Stalin ; a. Future Industries Institute, University of South Australia, Mawson Lakes 5095, Adelaide, South Australia, Australia, Engineering Ramadass, Kavitha; The University of Newcastle, Global Innovative Center for Advanced Nanomaterials (GICAN), Faculty of Natural Built Environment and Engineering Singh, Gurwinder; University of South Australia, Future Industries Institute Scaranato, Jey; Saudi Basic Industries Corp, SABIC Corporate Research and Development Center at KAUST Ravon, Ugo; Saudi Basic Industries Corporation Al-Bahily, Khalid; Saudi Basic Industries Corporation, SABIC Corporate Research and Development Center at KAUST Vinu, Ajayan; Global Innovative Center for Advanced Materials Faculty of Natural Built Environment and Engineering University of Newcastle

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Recent advances on functionalized micro and mesoporous carbon materials: synthesis and applications

a† a,b† a a figReceived 00th January 20xx, Mercy R. Benzigar, Siddulu Naidu Talapaneni, Stalin Joseph, Kavitha Ramadass, Gurwinder Accepted 00th January 20xx Singh,a Jessica Scaranto,c Ugo Ravon,c Khalid Al-Bahily,c and Ajayan Vinua,b*

DOI: 10.1039/x0xx00000x Functionalized nanoporous carbon materials have attracted the colossal interest of materials science fraternity owing to their intriguing physical and chemical properties including well-ordered porous structure, exemplary high specific surface www.rsc.org/ areas, electronic and ionic conductivities, excellent accessibility to active sites, and enhanced mass transport and diffusion. These properties make them a special and unique choice for various applications in divergent fields such as energy storage batteries, supercapacitors, energy conversion fuel cells, adsorption/separation of bulky molecules, heterogeneous catalysts, catalyst supports, photocatalysis, carbon capture, gas storage, biomolecule detection, vapour sensing and drug delivery. Because of the anisotropic and synergistic effects arising from the hetero atom doping at the nanoscale, these novel materials show high potential especially in the electrochemical applications such as batteries, supercapacitors and electrocatalysts for the fuel cell applications and water electrolysis. In order to gain the optimal benefit, it is necessary to implement the tailor made functionalities in the porous carbon surfaces as well as in the carbon skeleton through the comprehensive chemistries. These most appealing nanoporous carbon materials can be synthesized through the carbonization of high carbon containing molecular precursors by using soft or hard templating or non-templating pathways. This review encompasses the approaches and the wide range of methodologies that have been employed over the last five years on the preparation and functionalisation of the nanoporous carbon materials via incorporation of metals, non-metal heteroatoms, multiple heteroatoms, anchoring of various surface functional groups that mostly dictate their place in a wide range of practical applications.

fabrication of carbon nanotubes or fullerenes put the hurdle in 1. Introduction exploiting their full potential in various applications. On the other hand, the preparation of highly ordered nanoporous Design of carbon materials with ordered porous structure is one carbons is quite simple and the properties of these materials are of the hot topics in the area of materials chemistry. The high much better than other porous carbon materials owing to their specific surface area, large pore volume, well-ordered and ordered porous structure. Most importantly, the well-ordered controllable porous structure, unique morphologies of carbons porous structures support the addition of new functionalities and their excellent chemical, mechanical and thermal stabilities including organic or inorganic or biomaterials inside the porous attract them for various applications including energy storage channels or on the surface of the carbon walls, which and conversion, catalysis and sensing.1-4 Generally, carbon significantly enhance their performances in various nanotubes, fullerenes and ordered nanoporous (micro and applications. mesoporous) carbons have been widely applied for the energy Highly ordered nanoporous carbon materials have been and environmental applications including as adsorbents for the traditionally used for many years in large number of practical purification of water and capture of greenhouse gases.5, 6 applications including catalysis, energy storage and conversion, However, the complex synthesis methods required for the adsorption and separation and biomedical engineering. The first report on the preparation of highly ordered mesoporous carbon (CMK-1) via nanocasting approach led to a new class of ordered a. Future Industries Institute, Division of Information Technology Energy and mesoporous carbons (OMCs), with large specific surface areas Environment, University of South Australia, Adelaide, SA 5095, Australia. 1, 7 b. Global Innovative Center for Advanced Nanomaterials (GICAN), Faculty of and tunable pore diameters between 2 and 50 nm. This Engineering and Natural Built Environment, The University of Newcastle, invention has led to the discovery of many useful porous Callaghan, NSW 2308, Australia. E-mail: [email protected] materials including carbons, polymers, metal oxides, silicas and c. SABIC Corporate Research and Development Center at KAUST, Saudi Basic metals which are considered as potential game changers for Industries Corporation, Thuwal 23955, Saudi Arabia. various current technologies.1, 7 The structure of these †These authors contributed equally. nanoporous materials can be controlled by varying the structure of the templates used for the synthesis. For example,

several mesoporous silica materials with different structures

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including MCM-48, SBA-1, SBA-15, SBA-16, KIT-6 and KIT-5 have emission, optical, electronic devices and fuel cells. Therefore, been used as templates for the fabrication of mesoporous the research on the development of ordered nanoporous carbon materials (CMK-x) with different mesoporous carbons with different functional groups is being actively structures.8-12 A similar nano-hard templating approach was progressed for energy and electrocatalytic applications. Several also used by Hyeon et al. for the preparation of ordered porous review articles have been reported on the preparation of pure carbon using phenolic resin as the source of carbon.13, 14 OMCs mesoporous carbons and their applications.4, 18-21 However, the having surface areas of more than 2000 m2 g−1, a higher pore review papers on the recent development on the preparation, volume of up to 3.0 cm3 g−1 and tuneable pore diameters along functionalization and applications of nanoporous carbon with high conductivities can be achieved through a nanohard materials are quite limited.21 For instance, much progress has templating approach using mesoporous silica hard-templates. been made recently on the conversion of metal organic Because of their excellent textural characteristics, physical frameworks (MOFs) in to highly dispersed metal/metal oxide properties and chemical stability, OMCs have been productively functionalized nanoporous carbons without any external utilized in carbocatalysis, adsorption and separation of toxic sacrificial templates for energy related applications.21-23 molecules, gas storage, selective sensing, energy conversion In this review, we give an overview on the latest advances in fuel and solar cells, batteries, super(ultra)capacitors, and synthesis, structural characteristics, physicochemical properties biomedical devices.4, 15-17 The properties and the performance and the prospects for application of pristine and functionalized of these OMCs can be controlled with the modification of OMCs (Table 1). Much emphasis will be given on the relatively porous structure with organic or inorganic moieties. For new and exciting discoveries on the nanoporous materials with example, the introduction of foreign atoms such as B, N, O, S different organic or inorganic functional moieties such as B, N, and P in the carbon framework can tune not only the specific O, S and P, amines, complexes and hybrid OMCs incorporated surface area and electronic properties of the materials but also with metal nanoparticles, metal oxides, metal chalcogenides their performance in catalysis or sensing. These factors are and graphene. We also address how these added functionalities critical for various applications including semiconducting, field may affect the final performance of the materials in various

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applications including sensing, drug delivery, carbon capture, mesoporosity in carbon materials can be easily introduced by energy storage and conversion and adsorption and separation nanocasting technique using mesoporous inorganic materials (Fig. 1). New developments on the ways to improve the such as mesoporous silica and zeolites as hard templates. properties and performance of varieties of functionalized Various mesoporous carbons with different textural properties nanoporous carbon reported during the last five years are also have been prepared by using different porous templates described in detail with the aim of demonstrating the through this simple technique and the details of the materials uniqueness and the real academic and market potential of these and the structural parameters are given in Table 1. Although materials. Finally, new directions and the development of these many materials have been prepared, the control of structure nanostructures and the extension of the application of these and morphologies of the materials has been gaining a significant materials even in the wide range of applications are described attention owing to the correlation with their final textural in the conclusion and outlook. parameters. To control the morphology of the final OMCs, it is necessary to control morphology of the template materials. Schuster et al. reported that the spherical OMC nanoparticles 2. Synthesis Methods with bimodal pore size distribution having mean pore sizes OMCs and hetero atom doped OMCs are generally prepared by centred at 6 and 3.1 nm having 300 nm diameter via nano using templating strategies. Two well-established templating templating approach can be prepared by using the phenol and techniques such as hard and soft templating methods are formaldehyde mixture precursor and spherical silica as a hard 24 employed for the synthesis of OMCs and hetero atom doped template. The material showed high specific surface areas of 2 −1 3 OMCs. In the soft-templating method, the ordered mesoporous 2445 m g and the highest inner pore volumes up to 2.32 cm −1 framework structure is achieved by the cooperative assembly of g . In this case, the shape of silica hard templates has been amphiphilic surfactant molecules and precursor moieties. In this prepared by using a 400 nm PMMA spheres with close packed case, mesoporosity is generated upon removing the surfactants opal structure. This unique structure has been replicated into through the calcination process at high temperatures. The the final nanoporous carbon samples. The typical spherically nanocasting method is rather a conventional templating ordered opal structures of OMCs with large domains of process, but the scale of production is in a nanoscale order. In nanoparticles are shown in the TEM images and DLS the nano templating approach, highly ordered inorganic measurements. Seo et al. demonstrated the preparation of mesoporous solid materials are used to replicate their structure OMCs by using furfuryl alcohol (FA) as a carbon source and into nanoporous carbon materials with well-ordered phosphoric acid or sulfuric acid impregnated acidified 25 mesoporosity. There are several review articles outlining the mesoporous silica as a precursor. This work has been aimed at details of these synthetic processes including history, different preventing the generation of external carbon by selecting a synthetic strategies, and the formation mechanism for moderately weak acid that would slowly catalyze the obtaining ordered nanoporous carbons.2, 4, 7, 15 However, in the polymerization of FA. However, the obtained OMCs exhibited present review, we will discuss the recently reported synthesis lower surface area than OMCs prepared by using the methods and templating strategies applicable to OMCs from unmodified mesoporous silicas. the last five years. Hard templating approach can also be used to prepare nanoporous carbon in monoliths form. Hierarchical porous 2.1 Hard templating method for OMCs carbon monoliths (HPCMs) with both ordered hexagonal mesoporosity and three-dimensionally connected Hard templating approach is considered as one of the most macroporosity, and controlled morphologies have been straightforward ways for synthesizing OMCs.7 Ordered synthesized via a simple nanocasting pathway by using hierarchically macro/mesoporous silica with tunable morphologies as a hard template and FA and trimethyl benzene (TMB) mixture as a carbon a source. These monoliths exhibit high pore volumes (1.6 cm3 g−1) and specific surface areas (1354 m2 g−1) and a strong hydrophobicity due to the nature of the precursor used in the synthesis.26 These results reveal that the selection of the precursors is the key to control the surface characteristics of the final carbon materials. OMCs with various surface areas of 1361 to 3840 m2 g−1 and tunable micropores have been prepared by using zeolite Y and zeolite EMC-2 as sacrificial hard templates and FA as the precursor.27, 28 Although FA was used as the precursor for zeolite templated porous carbons, the pores of the zeolites are too small to accommodate bulky molecular precursors. Ryoo et al. has tackled this problem by using ethanol as a carbon source and hierarchical meso-/microporous zeolite beta as a template for the synthesis of hierarchical nanoporous carbons with

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mesopores into micropores. The properties of the OMCs can also be significantly altered with the external agents such as metal oxides. Ryoo and his co-workers realized this wonderful opportunity and demonstrated a ground breaking lanthanum-catalysed zeolite templated synthesis process of microporous 3D graphene-like carbon materials using ethylene as a carbon precursor, which have two times higher conductivity than that of CMK-3 (Fig. 3).35 This is an energy efficient synthesis process as it requires carbonization temperature of only 600oC, whereas the conventional microporous graphene synthesis uses the temperature in the range of 900 to 1000 oC. Noteworthy, microporous carbon deposition in lanthanum modified zeolite Y occurs more than 20 times faster than in an acidic HY zeolite. Acetylene gas can also be used instead of ethylene to construct carbon frameworks by using modified zeolites. As acetylene gas is more reactive than ethylene, carbon deposition can be accomplished even at lower temperatures as low as 340 °C.35 If the realized microporous carbon materials possess poorly ordered porous structure, it becomes highly ordered nature after heat treatment of 900oC.36 The same group has also developed a large scale (70 g batch) synthesis of 3D graphene- like ordered microporous carbon with 2770 m2 g-1 BET surface area and 1.32 cm3 g-1 of pore volume by using the cost effective calcium modified zeolite X template and ethylene gas under the same conditions.37 These zeolite templated carbons (ZTCs) have a higher particle density, and higher surface area (around 3000 mesopore–micropore hierarchy.29 The hierarchically porous m2 g-1) than CMK-3. The gravimetric and volumetric surface carbons exhibited a high BET surface area of 2220 m2 g-1, large areas of ZTCs are the highest among all the carbon materials, micropore volume of 0.62 cm3 g-1 and mesopore volume of 1.48 therefore they exhibit a superior capacity for energy storage. cm3 g-1. The authors concluded that the ethanol precursor is These approaches demonstrated that the preparation strategy more suitable for the hierarchical carbon synthesis, as is the key to control the final properties of the OMC which compared with propylene or acetylene gas precursors, which is ultimately determine their performances in various mainly because of the formation of water vapour due to the applications. Although these materials have interesting decomposition of ethanol during the heat treatment. It is also properties, the main issue that gives hurdle in the path of their assumed that this process assisted in delaying the deposition of commercialization is the removal of the mesoporous silica and carbons at the exterior. Nueangnoraj et al. reported on the zeolite hard templates by highly toxic HF. Therefore, the formation of cross linked fullerene like three dimensional researchers found eco and environmentally friendly soft graphene based ordered microporous carbon with surface area templating approaches to prepare OMCs without of 2100 m2 g-1 in the confined nanochannels of zeolite Y by using compromising the textural parameters. acetylene gas through a pulsed chemical vapour deposition technique.30 Mokaya et al. introduced an elegant approach to synthesise 2.2 Soft templating method for OMCs 2 -1 porous carbons with ultra high surface area of 3332 m g and A soft-templating approach has been widely applied for the 3 -1 a specific pore volume of 1.66 cm g through a simple synthesis of various mesoporous materials including zeolites, impregnation of zeolite13X with FA followed by the chemical silica, inorganic metal oxides and mesoporous carbons.38-44 31 vapour deposition (CVD) of ethylene gas. This unique double Preparation procedures for the silica, zeolites and metal oxides filling approach introduced graphene sheets with a large have been well established.45, 46 However, the direct synthesis number of edges within the nanochannels and are responsible of OMCs by soft-templating approach is not straightforward. for enhancing the specific surface area of the final carbons. The Various factors including the15 functionalization of templates same group also demonstrated a pressure assisted strategy to with the polymeric units, hydrogen bonding between the create microporosity within the porous carbons derived from template and the precursors, organic-organic composites, 32,33, 34 zeolitic imidazolate framework (ZIF) templates. This organic-organic self-assembly, and hydrogen bonding induced simple compaction technique can be used as an effective organic-organic self-assembly have been optimized to obtain method to either increase or decrease the textural properties OMCs with excellent textural parameters.41, 47 of the activated ZIF-templated carbons as it has the potential to create new micropores or decrease the size of the large

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Journal Name ARTICLE Table 1. Summary of the synthesis conditions, heteroatom contents and textural parameters of the functionalized nanoporous carbons and their application possibilities. o Material Template precursor T ( C) Hetero Structure and morphology dpore SABET VTotal Applications Ref. and porogen atom (nm) (m2 g-1) (cm3 g-1) content OMC Silica inverse Phenol and 900 -- • Spherical shape 3.1 2445 2.63 • Li-S battery 24 spheres opal spheres formaldehyde nanoparticles 6.0 • 2D-hexagonal mesostructure • P6mm symmetry 27 TC-Y1 Zeolite Y Formaldehyde 900 -- • Fd3m symmetry 0.7-4 3519 1.3 • CO2 adsorption and Propylene • Nanoparticles 27 TC-Y2 Zeolite Y Propylene 900 -- • Fd3m symmetry 0.7-4 1815 1.8 • CO2 adsorption • Nanoparticles 27, TC-EMC Zeolite EMC- Formaldehyde 900 -- • P63/mmc symmetry 0.7-4 3840 1.8 • CO2 adsorption 48, 49 2 and Propylene • Retained EMC-2 zeolite morphology HR-ZTC Hierarchical Ethanol 600- • Nano particles 1.2 2220 2.45 • Supercapacitor 29 zeolite beta 700 • Zeolite morphology P7 Zeolite Y Acetylene 900 • Core-shell structure 1.0 2100 -- • Supercapacitor 30 31 FA-ZTC Zeolite 13X FA and 700 • Zeolite particle type 1.2 3332 1.66 • H2 storage ethylene morphology 32 CB-700 ZIF FA 700 • Nanoparticles (50-100nm) 0.8 970 0.66 • H2 uptake and acetonitrile • ZIF morphology HPCMs Hierarchical Furfuryl alcohol 850 -- • Positive replicas of 3.36 729- 1.6 • Cleaning/recycling 26 SBA-15- and trimethyl SBA-15-monolith 1354 spilled oils or organic monolith benzene • Rod shaped morphology solvents. • Bilirubin adsorption OMCs Pluronic F127 Resorcinol and 700- -- • Graphitic tubules 4.8 603-808 0.55- • Supercapacitors 50 and formaldehyde 1000 morphology 0.66 Fe(NO3).9H2O • P6mm symmetry OMCs Pluronic Resorcinol and 800 -- • Fm3m symmetry 10.1- 212-780 0.19- • Stabilization of Ag 51 F127, TEOS formaldehyde • Hexagonal arrangement of 11.0 0.65 nanoparticles and AgNO3 pores Monolithic Pluronic F127 Resorcinol and 600 -- • 2D hexagonal p6mm 4.7- 675-758 0.14- • Dehydrogenation of 52 mesoporo and formaldehyde symmetry 5.1 0.16 propane to propylene us carbons Citric acid OMC films Pluronic F127 Phenol and 350- -- • Cage type cubic Im3m • Kr sorption 53 formalin 800 • 2-D hexagonal p6mm • Face centered orthorhombic Fmmm NMC-G SBA-15 Gelatin 600- N: 4.5 to • 2D-hexagonal 3.54- 764-846 1.14- • Sensing of acetic acid 54, 55 1000 14.46 mesostructure 6.41 1.50 • CO2 adsorption at% • P6mm symmetry • Electrocatalyst for • Rod shaped morphology ORR OMFLC-N SBA-15 FA and 1000 N: 8.2 to • 2D hexagonal “crystal” 1.8- 1580 2.2 • Supercapacitrors 56 dicyandiamide 10.6 • P6mm symmetry 4.0 at% NOMC and SBA-15 Honey 650- N: 1.0 to • SBA-15 replicated 621- 0.73- • Metal-free catalyst 57, 58 HNMC 950 3.5 at% structure 1273 1.16 for ORR • Rod shaped morphology • Li and Na ion • P6mm symmetry batteries N-OMC Crab shells Resole and 750 N: 4.6 to • 2D hexagonal 4.1- 516- 0.3-2.35 • Supercapacitors 59 and N- and Pluronic dicyandiamide 6.7 at% • P6m symmetry 15.0 1030 OMCNFA F127 • Nano fibre morphology NONC SBA-15 Dopamine 800 N: 5 at% • Successful SBA-15 3.8 1013 1.14 • Supercapacitors 60 replication • P6mm symmetry • Rod shaped morphology G-OMC Mesoporous Dopamine 900 N: 1.6 • 2D morphology 3.5 269 0.35 • Electrochemical 61 NiO at% • Ordered graphitic double layer mesopores capacitors N-HMCs KIT-6 (1-methyl-1H- 850 N: 0.5 to • Well-ordered mesopores 3.4- 780- 0.91- • Electrocatalyst for 62 pyrrole-2- 10.0 • Successful transformation 4.0 1150 1.02 ORR towards H2O2 yl)methanol at% of KIT-6 type structure production • Ia3d symmetry N-HMCSs Mesoporous polystyrene/pol 700 N: 3.6 • Hollow structure 4.1 807 0.87 • Supercapacitors 63, 64 silica spheres yacrylonitrile at% • Mesopores on the shells NHPCM Amine Furfuryl alcohol 700- N: 1.1 to • Carbon rod replicas 3.8 744-796 1.31- • Electrocatalyst for 65 grafted 1000 1.5 at% • Well retention of 1.53 ORR hierarchical monolith morphology porous silica • Highly regular arrays of monolith branched morphology N-MC Amine Sucrose 900 N: 0.6 to • Hexagonally ordered 5.14 749-790 0.65- • Supercapacitors 66 functionalize 1.5 at% cylindrical mesopores 0.86 d SBA-15 • Negative replica of SBA-15 NOMC and SBA-15 Pyrrole or 800- N: 0.5 to • Inverse replica of the SBA- 3.7- 591-886 0.52- • Electrocatalyst for 67-69 C-PY aniline 1400 10.7 15 template 7.4 0.93 ORR at% • Highly ordered mesopores • Supercapacitors • P6mm symmetry NOMC SBA-15 D(+)-glucose 900 N: 2.5 to • stripe like mesopores 3.9- 352- 0.59- • Supercapacitors 70 and D- 3.9 at% • Rod shaped morphology 7.3 1152 0.97 glucosamine • P6mm symmetry This journal is © The Royal Society of Chemistry 20xx J. Name., 2013, 00, 1-3 | 5

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N-OMCs SBA-15 m- 700 N: 7.8 to • Pore channels arranged in a 5.0 1058- 1.0- • Ibuprofen (drug) release 71 aminobenzoic 8.3 at% bidimensional ordered array 1322 1.8 acid and p- • P6mm hexagonal symmetry aminobenzoic acid HPC-Ns Hierarchically FA, oxalic acid 750- N: 1.8- • Disordered hierarchical 3.5 1571- 1.5- • Electrocatalyst for ORR 72 porous silica and urea 900 6.4 at.% porous structure - 2473 2.2 monolith • Rod shaped morphology 3.6 NHPC-3D Silica spheres Dopamine 800 N: 7.4 • Interconnected and layered 2.5 1056 2.56 • Supercapacitors 73 at% • Macroporous structure N-OMCs SBA-15 Iron 900 N: 3.5- • Rugby ball or rice grain-like 3.1 1122- 1.6- • Electrocatalyst for ORR 74 phthalocyanine 3.7 at% ellipsoidal shape 1720 2.1 nanoparticles • Mesopore channels run parallel to the rod shape direction • P6mm hexagonal symmetry N-MCHSs Silica hollow Dopamine 600- N: 2.2- • Sponge like shells with 5.0 375- 0.40- • Anode for Li-ion batteries 75 spheres and 900 4.5 at% interconnection of hollow 438 0.43 Pluronic cores P123 • Carbon shells are interconnected by “carbon bridges” NMMC Pluronic F127 Resol and 700 N: 4.6- • 2D hexagonal meso- 4.6 1344 0.90 • Supercapacitors 76 and dicyandiamide 7.8 at% structure Titanium- • Highly ordered, stripe-like carbide pores 77 NMCs SBA-15 Amino acids 700- N: 3.6- • Ordered nanowire arrays 4.2 694- 0.89- • CO2 Uptake 900 9.4 at% • Rod like “wheats” shape 7- 1280 2.48 • Electrocatalyst for ORR morphology 5.7 • Ordered and disordered 2 mesoporous structure NMC SBA-15 Resol and 800 N: 5.1- • 2D Hexagonal mesostructure 2.4 1095- 0.73- • Supercapacitors 78 cyandiamide 15.1 • Shuttle-like morphology - 1722 1.81 at% • P6mm symmetry 4.1 NNCM 3D Polyacrylo 900 N: 6.1- • 3D continuous nano 30 391- 0.9- • Volumetric capacitors 79 continuous nitrile (PAN) 6.5 at% framework 663 2.1 skeleton • Numerous continuous silica mesopores particles 80-82 meso-BMP Ludox HS40 Ionic liquids: 900 N: 5.0- • Long-range ordered 5- 320- 0.75- • Electrocatalyst for H2O2 3DOm Slilica BMP-dca 17 wt% structure 20 1380 3.6 production carbon spheres EMI-dca • Pores are less well defined • Electrochemical double- EMI-tfsi layer capacitors RF-1 and Pluronic F127 Resorcinol and 350- N: 1.1- • Body-centred cubic (Im3m) 3.1 659- 0.33- • Adsorption 83 RF-2 and hexamethylene 900 6.5 at% to 2D hexagonal (p6m) - 870 0.49 Trimethylben tetramine structure 6.7 zene (HMT) • Irregular polyhedral particles Ammonia

84 PHMT -- Resorcinol and 600- N: 1.3- • Interconnected spherical 0.6 528- 0.19- • CO2 capture HMT hexamethylene 1000 6.9 at% particles - 936 0.33 ACMP-N tetramine • Nitrogen containing 1.3 (HMT) microporous carbon Ammonia 85 NOMC Pluronic F127 Resorcinol- 600- N: 2.4- • Body-centred cubic Im3m 2.7 583- 0.30- • CO2 adsorption melamine- 800 2.9 at% symmetry 1- 631 0.33 formaldehyde • Irregular polyhedral particles 3.0 resin 2 Nitrogen- Pluronic F127 Resorcinol 700- N: 7.1- • Highly ordered mesoporous 6.6 643- 0.57- • Supercapacitors 86 enriched formaldehyde 850 9.1 at% structure - 1415 1.2 OMCs NH3 gas • P6m symmetry 7.0 87 H-NMC Pluronic F127 Resol and 600 N: 0.09 • Tunable mesostructures 3.1 494- 0.14- • CO2 capture C-NMC dicyandiamide to 13.1 (p6m and Im3m symmetry) - 586 0.17 • Supercapacitors wt% • Mesostructure formed in a 17. layer-by-layer fashion 6 N-OMCs Pluronic F127 Resorcinol 600 N: 0.23 • Parallel mesoporous 5.5 376- 0.42- • Dehydrochlorination of 88-90 and Na2CO3 formaldehyde to 4.2 channels - 718 0.78 1,2-dichloroethane dicyandiamide wt% • Well retention of 9.3 mesoporous structure • 2D P6mm hexagonal symmetry N-OMCs Pluronic F127 Urea-phenol- 600 N: 0.38 • Spherical morphology 2.1 446- 0.24- • Adsorbent for acidic gases 91-93 formaldehyde to 1.41 • Cubic Im3m mesostructure 566 0.31 • Electrochemical capacitors wt%

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94, 95 om- MR Pluronic F127 Phenolic- 400 N: 18.16 • Ordered mesostructured of 2.9 385.9 0.17 • CO2 Adsorption functionalized wt% Im3m symmetry • Supercapacitors melamine resin • Polyhedron shape morphology NPGC Pluronic F127 Glucose and 800- N: 2.9- • Nanosheet-like structure 4.8 579- 0.38- • Supercapacitors 96 TEOS, nickel melamine 1000 6.96 • Interconnected nanoporous - 1116 0.79 nitrate wt% structure 6.3 N-doped Pluronic F127 Resol and 700 N: 5.74- • Hexagonal pore arrangement 5.1 631- 0.4- • Supercapacitors 97 OMC TEOS dicyandiamide 8.1 wt% • Stripelike 2D mesostructure - 1374 1.5 7.4 NMNC -- Glucose and 800- N: 2.6- • Sphere structure 2.3 1154- 0.67- • Electrocatalyst for ORR 98 NH3 1000 4.7 wt% • Network-like morphology - 2588 1.71 2.8 NMC5 Pluronic F127 Resorcinol 700- N: 5.5- • Sphere shape morphology 5.0 307- 0.30- • Electrocatalyst for ORR 99 and formaldehyde 1000 25.7 • Ordered porous structure 484 0.41 Fluorocarbon Melamine wt% NOMC Pluronic F127 3-aminophenol 800 N: 3.4- • Polyhedral crystal like 3.6 72- 0.05- • Supercapacitors 100 hexamethylene 5.4 wt% morphology - 1159 0.72 tetramine • Rhombic dodecahedron 5.4 (HMT) shape Ammonia • m3m symmetry NMC Pluronic Melamine- 600- N: 5.5- • Disordered porous structure 5.0 252- 0.31- • Electrocatalyst for ORR 101 P123 formaldehyde 900 27.1 794 1.15 Sodium resin wt% silicate NHCSs Pluronic 2,4- 800- N: 3.6- • Ruptured spherical particles 3.9 738- 0.5- • Electrocatalyst for ORR 102 P123 dihydroxybenzo 1000 7.8 at% • Hollow spherical structures 820 0.56 Sodium ic acid and oleate hexamethylene tetramine (HMT) BOMCs SBA-15 sucrose and 4- 900 B: 0.64- • 2D hexagonal mesoporous 6.4 778- 1.18- • Electrocatalyst for ORR 103, 104 hydroxyphenylb 2.11 structure - 1040 1.52 oronicacid at% • P6mm symmetry 7.2 • Rod-like particles Mesoporo Pluronic F127 Phenol, 400- B: 3.6 • 2D hexagonal mesoporous 3.6 475- 0.45- • Proton exchange 105 us CB film formalin and 700 at% structure - 551 0.53 membrane fuel cells boric acid 4.1 Hierarchic Pluronic F127 Resorcinol and 800 B: 0.42- • Hierarchical mesoporous 5.0 547- 0.49- • Supercapacitors 106 al carbons boric acid 2.37 structure 643 0.73 with boron at% • Ordered pores POMCs SBA-15 Phenol and 900 P: 1.36 • Spherical carbon 3.5 814- 1.4- • Electrocatalyst for ORR 107 triphenylphosp at% microstructures 1182 1.87 hine • Highly ordered uniform pore distribution POMCs SBA-15 Glucose and 900 P: 0.64 • Rod shape morphology 3.8 1117- 1.24- • Pt nanoparticles 108 triphenylphosp at% • P6mm symmetry - 1338 1.37 stabilization hine 4.3 • Methanol electrooxidation SN-OMCs SBA-15 Thiophene and 700 N: • 2D hexagonal mesoporous 3.5 750- 0.53- • Electrocatalyst for ORR 109 pyrimidine 6.2at% structure 1100 0.83 • Rod like morphology S: 0.25 • P6mm symmetry to 0.68 at% NSOMC SBA-15 Pyrrole and 650- N: 4.8 to • 2D hexagonal mesoporous 3.2 978- 1.1- • Electrochemical double- 110 H2SO4 950 10.0 structure 4 1021 1.2 layer capacitor at% • Rod like morphology • P6mm symmetry S: 1.7 to 2.6 at% SNOMC SBA-15 Pyrrole and 800 N: 1.2 to • 2D hexagonal mesoporous 6.2 601 1.0 • Electrocatalyst for ORR 111 thiophene 5.7 at% structure • Rod like morphology S: 5.6 to • P6mm symmetry 8.7 at% SN-OMC SBA-15 Diphenylthiocar 800- N: 3.2 • 2D hexagonal mesoporous 5.1 647- 0.5- • Electrocatalyst for ORR 112 bazone 1000 at% structure 816 0.75 • Rod like morphology S: 0.8 • P6mm symmetry at% OMC-S SBA-15 Sucrose and 900 S: 1.4 to • 2D hexagonal mesoporous 4.5 1099- 1.37- • Electrocatalyst for ORR 113 benzyl disulfide 1.5 at% structure - 1244 1.61 • Rod like morphology 5.4 • P6mm symmetry HTBP Pluronic F127 Resorcinol, 600 B: 0.8 to • Ordered mesostructured 6.2 590- 0.59- • Supercapacitors 114 boric acid and 1.6 at% 659 0.67 phosphoric acid P: 2.3 to 3.6 at% O: 8.1 to 10.0 at% This journal is © The Royal Society of Chemistry 20xx J. Name., 2013, 00, 1-3 | 7

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Among these strategies, the direct synthesis of OMCs using carbonization temperature has been observed for thin film organic–organic self-assembly involving the combination of samples and the process changes the space group of the polymerizable precursors and block copolymer templates is obtained films. On the other hand, only unit cell parameters expected to be more flexible than other soft templating were reduced for the powder samples upon alteration of methods and the traditional hard templating nanocasting carbonization temperature while keeping the original space methods.47 Li et al. reported a series of hexagonally ordered groups by isotropic shrinkage with condensation of the mesoporous carbons (OMC-Ts) by adjusting the pyrolysis framework. This unique approach involving a simple adjustment temperature of resorcinol and formaldehyde mixture via a soft of the preparation conditions, the amounts of Pluronic F12, and templating and catalytic graphitization approach by using the the carbonization temperature is found to be the effective tool

Pluronic F127, EO106PO70EO20 triblock copolymer as the for controlling structure of the OMC films. 50 template and Fe(NO3).9H2O as a catalyst. The structure of OMC-Ts has a two-dimensional hexagonal (p6mm) mesostructure with tubule like morphology. The OMC-700 3. Hetero atom doped OMCs sample synthesized at 700 ˚C showed a high specific surface Heteroatom doping is the replacement of some of the carbon 2 −1 3 −1 area of 808 m g , and pore volume of 0.55 cm g with a atoms in the uniform graphitic carbon structure with other uniform mean pore size of 4.8 nm. foreign atoms which significantly changes the electronic, Sterk et al. described a soft-templating synthesis procedure electrical and surface charge properties of the final materials. 2 −1 to prepare OMCs with BET surface area up to 780 m g using The introduction of heteroatoms such as boron, nitrogen, triblock copolymer F127 and phenolic resin precursors in the sulphur, and phosphorus into the OMCs could cause electron presence of tetraethyl orthosilicate (TEOS). In this case, silver modulation due to their different electronegativity. This also nitrate was added in the synthesis mixture to increase the tunes their charge distribution, optoelectronic properties microporosity as well the metal nanoparticles in the porous and/or defect induced chemical functionalities, which are 51 channels of OMCs. Monolithic mesoporous carbons were also useful for many technological applications.115, 116 Heteroatom- prepared from resorcinol–formaldehyde resin through a simple doped OMCs can be prepared either by in-situ doping during autoclaving method using citric acid as a catalyst and triblock the preparation of nanoporous carbon materials or through copolymer F127 as a structure directing agent. The obtained post-treatment of preformed carbon nanomaterials with mesoporous carbons have a hexagonal pore system, uniform heteroatom-containing precursors.117 Post treatment 2 pore size of 5.0 nm and a high BET surface area of 758 m procedure often leads to only surface functionalization without −1 52 g . Similar strategy was also adopted to make highly ordered altering their bulk properties whereas the in-situ doping of ∼ ∼ OMC films with controllable mesostructures and highly hetero atoms can help to homogeneously incorporate the accessible surfaces. A simple direct carbonization of phenolic heteroatoms into the entire nanoporous carbon matrix. resin and the conventional Pluronic F127 and EO106PO70EO20 triblock copolymer as a template afforded the highly ordered 3.1 Nitrogen doped OMCs OMC films (Fig. 2).53 The structure of the films can be controlled Nitrogen is one of the neighbour elements next to carbon in the by adjusting the amount of the surfactant in the synthesis periodic table and it has an atomic radius similar to that of mixture. Unique concept of mesostructural transformation of carbon but has different electronic configuration and cage-type to tubular frameworks via anisotropic shrinkage upon electronegativity.117 Thus, nitrogen doping into the OMCs could increasing the carbonization temperature was also change their electronic structures while minimizing the lattice demonstrated.40 Anisotropic shrinkage upon increasing the mismatch, leading to unique electronic properties. Great efforts have been paid to introduce nitrogen atoms into OMCs as the incorporation of nitrogen atoms into the nanoporous carbon matrix can significantly enhance their conducting, field emission, catalytic, and energy storage properties.118-132

3.1.1 Hard templating approach The precursors containing N atoms including polymeric compounds, acetonitrile, urea, aromatic or aliphatic amines are generally used in combination with the hard-templating method for the incorporation of nitrogen in the carbon framework of OMCs.133, 134 Recently, Vinu et al. demonstrated the synthesis of highly ordered nitrogen-containing mesoporous carbon (NMC-G) with well-ordered mesopores and various pore diameters and also high basicity using a low-cost, naturally occurring gelatin biomolecule as a single-molecule precursor and 2D hexagonal SBA-15 with different pore

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diameters prepared at different hydrothermal temperatures SBA-15 (9.1 nm) but similar to the wall thickness, revealing the were used as the hard templates (Fig. 4).54, 55 transformation of silica walls into pores and the pores of the The realized NMC-G materials have excellent textural templates into N-doped carbon walls.57, 58 NOMC nanofiber properties such as high specific surface areas (764-804 m2 g−1), array was prepared by a combination of a soft templating huge pore volumes (1.14-1.40 cm3 g−1), and mesoporous method in combination of hard-templating approach using a diameters (3.54-4.89 nm). Recently, Huang et al. made the well-mixed solution of calcined crab shells, Pluronic F127, ground breaking discovery on synthesis of self-supported N- dicyandiamide (DCDA) and resole.59 NOMC nanofiber arrays doped ordered mesoporous few-layer carbon (OMFLC-N) super possessed four resolved SAXS scattering peaks, which were structures catalysed by Ni catalyst through chemical vapour indexed as the 100, 110, 200, and 210 planes of a 2D hexagonal deposition using a simple and environmentally friendly mesostructure with a space group of p6m. The obtained NOMC precursors such as FA and dicyandiamide (DCDA) and nanofiber material also exhibited a high surface area (1030 m2 mesoporous SBA-15 silica as the template.56 OMFLC-N sample g−1) and a large pore volume (2.35 cm3 g−1), with uniform exhibited a high conductivity (360 S cm-1) with mesoscopically mesopores of ca. 15.0 nm which was much larger than that of ordered few-layers and also possessed the largest surface area CMK-3s, OMFLC-N, and NOMCs.1, 56-58 These reports clearly (1580 m2 g−1), a high total pore volume (2.20 cm3 g−1), the reveal that the natural biomasses are the unique and low cost smallest average pore width (2.25 nm), and the most prominent sources for the in-situ introduction of nitrogen atoms in the pores smaller than 2 nm. Graphene-like structure with ≤5 layers carbon framework of OMCs which could offer exciting and minimum number of defects in OMFLC-N were verified by electronic properties. Raman spectroscopy. The introduction of transition metal ions Although natural biomasses used for the heteroatom doped helps the formation of highly graphitic structure along the walls nanoporous carbons are cost effective, the control of the whereas the N doping changes the electronic structure of the degree of polymerization is highly difficult. This has been formed carbons. The combination of these factors significantly addressed by the judicious choice of easily polymerisable enhances the conductivity of the final materials. precursors. A facile synthesis route has been developed to Natural biomass honey which contains 80–85% of prepare nitrogen-doped ordered nanoporous carbons (NONCs) carbohydrates, 15–17% water, 0.3% proteins, 0.2% ashes and by Wu et al. based on in situ polydopamine coating onto the minor quantities of amino acids and vitamins have also been SBA-15 pore surface.60 The dopamine was quickly self- utilized as the source of nitrogen and carbon for the fabrication polymerized onto the pore wall of SBA-15, forming of nitrogen-doped ordered mesoporous carbons (NOMCs). Guo polydopamine/silica nanocomposites in the presence of tris- et al. and Xiao et al. have independently demonstrated the buffer solution. The carbonization of the polydopamine/silica

synthesis of NOMCs by nanocasting method using SBA-15 as the nanocomposite in N2 and then removal of the silica template template and natural honey as a source for nitrogen and carbon eventually led to the formation of NONC material with a BET (Fig. 5). The structure of NOMCs exhibited two-dimensional surface area of 1013 m2 g−1. However, these materials suffered hexagonal mesoporous framework, composed of ordered from poor crystallinity which suppress the conductivity of the nitrogen doped carbon nano rods. The BET specific surface materials. This was overcome by the discovery of Yuan et al. areas of NOMCs were in the range of 600 to 1100 m2 g−1 but who reported the synthesis of nitrogenated graphitic ordered varied significantly with the change of carbonization mesoporous carbon (G-OMC) by using mesoporous nickel oxide temperature. It should be noted that the pore size of NOMCs is as a template as well as the catalyst and dopamine as a 4.0 nm, which is less than half of the mesoporous silica template precursor. The results revealed that G-OMC materials had a higher degree of graphitization than those prepared from dopamine and pure SBA-15 as the template, which was mainly because of the catalytic graphitization induced by the nickel

oxide catalyst. The ID/IG value of the G-OMC was 0.69, which was much less than that of the ID/IG value of CMK-3 (0.84), revealing the high graphitic nature of G-OMC.61 For many applications, not only the conductivity but also the amount of nitrogen doping in the carbon framework is also crucial as it sometimes dictates the final performance of the materials. For instance, Park et al. demonstrated the synthesis of mesoporous nitrogen-doped carbon with tunable nitrogen content with a simple adjustment of the amount of the precursor, (1-methyl-1H-pyrrole-2-yl) methanol (MPM), which is structurally similar to FA, using 3D body centred cubic KIT-6 as a template. The nitrogen content of the resulting carbon was controlled in the range of 0−10 at. % and all prepared samples had well-ordered mesopores with diameters of 3.4−4.0 nm with BET specific surface areas of 780−1150 m2 g−1.62

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Nitrogen atoms have also been doped with OMCs with different morphologies using different techniques. For example, monodispersed nitrogen-doped hollow mesoporous carbon spheres (N-HMCSs) have been synthesized using a novel “dissolution-capture” method wherein the polystyrene/polyacrylonitrile composite nanospheres (PS@PAN) were used as the carbon and nitrogen resource, which were uniformly coated by a layer of mesoporous silica. After organic solvent treatment, the PS@PAN were dissolved and then captured in the confined nanospace of mesoporous silica shell. The N-HMCSs with the surface area and pore volume of 807 m2 g−1 and 0.87 cm3 g−1 were produced after the carbonization followed by the removal of the template through HF etching.63, 64 The orientation of the formed carbon nanorods can be controlled with the simple modification of the surface of the sacrificial template. Wang et al. reported an in situ source- template-interface reaction route to prepare 3D N-doped hierarchical porous carbon monolith (NHPCM) composed of catalysts in improving the graphitic nature and conductivity in branched mesoporous rods by nanocasting method with the the resulting materials. amine functionalized hierarchical porous silica monolith Aniline, pyrrole and phenanthroline, were also (NHPSM) scavenger and FA as the carbon source.65 It has been independently used as nitrogenated carbon precursors to demonstrated that this unique approach helped to anchor a synthesize NOMCs by the nanocasting method with SBA-15 high density of N atoms on the surface of the NHPCM as a template. The NOMC materials derived from pyrrole (C‐PY‐900: simple solid-solid interface reaction between the carbon 765 m2 g−1) and phenanthroline (C‐Phen‐900: 746 m2 g−1) precursors and amine functionalized NHPSM favoured the exhibited higher specific surface areas than the aniline analogue doping on the surface. Asefa et al. also described the NOMC but the nitrogen content of these samples was almost constant synthesis by using the amine groups functionalized mesoporous (3.1–3.3 at% ) for the three carbon sources, except for a slight silica SBA-15 but glucose was used instead of FA as a carbon difference in the nitrogen configuration.135 NOMC catalyst was precursor.66 By varying the nature of the solvents (polar or non- directly synthesized using SBA‐15 as a hard template, sucrose as polar) used for grafting amines on the surface of the templates, a carbon source and urea as the nitrogen source, respectively. the amount of N doping on the final NOMC was controlled. A 3.6 wt% of nitrogen doping in the NOMC was achieved with Liang and Tsiakaras et al. reported a novel impregnation more than 70% of the nitrogen incorporated as quaternary method, namely vaporization-capillary condensation process to nitrogen species.136 This is one of the best ways of controlling synthesize NOMC via nano hard templating method using SBA- nature of the nitrogen species on the wall structure of the 15 as the template and pyrrole as the precursor in the presence NOMCs. of FeCl catalyst. This new impregnation method yielded a much 3 Nitrogen doping was also tried in porous carbons with larger surface area (661 m2 g−1) and pore volume than the wet different pore diameters. Chen et al. reported on the synthesis incipient method (292 m2 g−1).67, 68 With the adjustment of the of nitrogen-doped micro-mesoporous carbon material with pore diameter of SBA-15 template and the carbonization surface area of 789-1367 m2 g−1 by employing urea- temperature, the textural parameters and nitrogen content of formaldehyde resin as carbon and nitrogen sources, zinc NOMCs prepared from pyrrole precursor were controlled, chloride as a porogen and SBA-15 as a hard template.137 respectively.69 NOMCs have also been synthesized by using a Nitrogen doped three dimensionally ordered microporous mixture of D(+)-glucose and D-glucosamine hydrochloride as carbon (N-ZTC) was also synthesized by using aqueous carbon precursors and SBA-15 as the template. The as-prepared acetonitrile as a nitrogen-containing carbon source, and zeolite products showed a large pore volume (0.59–0.97 cm3 g−1), high beta as a template. The obtained materials possess nitrogen surface areas (352.72–1152.67 m2 g−1) and rational nitrogen content of approximately 4 wt%, a large surface area and pore content (ca. 2.5–3.9 wt.%).70 In another study, Sanchez et al. volumes of 1860 m2 g-1 and 1.4 cm3 g-1, respectively.138 Ling et demonstrated the NOMCs synthesis by using SBA-15 and two al. reported on hard-templating synthesis of pristine and aromatic polyaramids namely, m-aminobenzoic acid (MABA) functionalized CMK-3 materials having BET surface areas in the and p-aminobenzoic acid (PABA) as the precursors for C and N.71 range of 1152 to 1760 m2 g−1 with various functionalities, NOMCs with different morphologies and a nitrogen content of including micropore development, nitrogen doping by using 3.5–3.7 at.% were also prepared by Yu et al. through the SBA-15 as the mesopore template, and silicate oligomer as the pyrolysis of iron phthalocyanine infiltrated in SBA-15 with micropore template, low-molecular-weight phenolic resins as different mesochannel lengths. The BET surface area was found the carbon precursors and nitrogen-rich to be decreased with increasing the mesopore channel length hexamethoxymethylmelamine (HMMM) as a nitrogen of the SBA-15.74 Transition metal containing precursors not only precursor.139 act as the source for the porous carbons, but also act as a

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Ahn et al. synthesized a series of ladder type nitrogen-doped dopamine precursor and mesoporous silica hollow spheres mesoporous carbons (CPANs), which was found to have a high template to prepare nitrogen doped mesoporous carbon stability, by using SBA-15 and in situ polymerization of hollow spheres (NMCHSs) with specific surface area of 411.6 m2 polyacrylonitrile (PAN) inside the mesochannels of template at g−1.75 Tang et al. developed an innovative method of the different carbonization temperatures. Among the materials sublimation and capillary condensation assisted nanocasting prepared, CPAN-800, synthesized at the carbonization method for the fabrication of Fe and N dual-doped mesoporous temperature of 800°C, was found to be the best one with many carbon catalyst with 988 m2 g−1 BET surface area and 0.87 cm3 desirable properties such as high specific surface area (1182 m2 g−1 pore volume. Easily sublimmable iron phthalocyanine was g−1) and pore volume (1.54 cm3 g−1), moderate nitrogen content used as the sources of iron, nitrogen and carbon, while of 9.52%, and highly ordered mesoporous structure with mesoporous silica SBA-15 has been used as the hard uniform pore sizes of 4.34 nm.140 Zhao et al. adopted a similar template.142 strategy but used a low molecular weight phenolic resin (resol) Nitrogen-doped mesoporous carbon spheres (NMCS) were as a carbon source and a high nitrogen-containing cyanamide as prepared by a nanocasting route using benzoxazine resins as the the nitrogen dopant. The prepared NOMCs exhibited a high precursor of nitrogen and carbon, and ordered mesoporous surface area of 1741 m2 g−1 and nitrogen content up to 15 wt% silica spheres as the hard template. The prepared NMCS by nanocasting approach. It was also demonstrated that the BET exhibited amorphous spherical nanoparticles with worm-like surface area (1397–1741 m2 g−1), pore size (3.6–4.1 nm) and mesoporous channels, the specific surface area, pore volume pore volume (1.05–1.81 cm3 g−1) were easily tailored by and nitrogen contents were 634 m2 g−1, 0.91 cm3 g−1 and 3.50 controlling cyanamide-to-resol mass ratio or the carbonization (wt%),respectively.143 Nitrogen-doped hierarchical temperature in the range of 600–900oC.78 Yang et al. used silica mesoporous/microporous carbon (NMMC) was also prepared gel template with 3D continuous skeleton and PAN in DMF by using nitrogen-doped mesoporous titanium-carbide/carbon solution for the synthesis of nitrogen-doped mesoporous composite, followed by removal of carbides with chlorination. carbon (NNCM) with the tunable pore volume of (1.22 to 2.11 The obtained NMMC gave a high surface area of 1344 m2 g−1 cm3 g−1) but a fixed pore size in order to control the coating and exhibited micropores that were drilled on the mesopore density for miniaturized energy devices. This was achieved by walls with the size of 0.70, 0.97 and 1.61 nm.76 the simple adjustment of the quantity of PAN in DMF in the Although the solvents play an important role in controlling mesochannels of the 3D template.79 3D NOMCs having BET the pore filling which is critical not only to control the nitrogen surface area up to 1131 m2 g−1 have been carried out using three content but also structural order of the materials but dimensionally ordered silica as the template and FA and oxalic sometimes it significantly increases the total cost of the acid as the carbon source and an acid catalyst, respectively production of the materials. Gao et al. described the synthesis under ammonia pyrolysis.141 of NOMCs with improved yields of up to 25% by direct heating Nitrogen doped hierarchically porous carbon materials of amino acids in inside porous channels of SBA-15 without (HPC-Ns) has been successfully synthesized by Shi et al. by using any solvent and metal catalysts. The diverse types of applying a simple N-doping procedure using FA, oxalic acid and amino acids, their variable interactions with SBA-15 and urea mixture in ethanol solution as a carbon and nitrogen different pyrolytic behaviours led to nitrogen-doped precursor and hierarchically macro/mesoporous silica as a mesoporous carbons with tunable surface areas (700–1400 m2 template. The synthesized HPC-N samples demonstrated 3D g−1), pore volumes (0.9–2.5 cm3 g−1), and pore sizes of 4.3–10 connected ordered mesoporosity with extremely large specific nm.77 surface area (2473 m2 g−1) and relatively high content of pyridinic N.72 It was clear that when the nitrogen precursor was combined with organic polar solvent, the specific surface area was significantly enhanced. 3D interconnected nitrogen-doped hierarchical porous carbons (NHPC-3D) were also prepared via a hard-templating method with colloidal silica spheres (80 nm) and dopamine as the template and precursor, respectively. One of the interesting features of this study was the use of dopamine as the nitrogen precursor and the utilization of large sized colloidal silica nanoparticles as templates. Dopamine has several advantages such as self and low temperature polymerization, easy interaction with the surface of any templates and the final total carbon yield after carbonization. In addition, the templates with large nanoparticles offered a 3D structure with macropores. The obtained NHPC-3D also exhibited a high surface area of 1056 m2 g−1, a large pore volume of 2.56 cm3 g−1, and a high nitrogen content of 8.2 wt%, which also revealed the presence of large quantity of micropores in the samples.73 Huo et al. also used

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Nitrogen doped mesoporous carbon (meso-BMP) was the soft templating approach is the interactions between the synthesized by Hasche et al. with the pyrolysis of high nitrogen structure directing agents and the nitrogenated precursor as it (17 Wt%) containing N -butyl- 3-methylpyridinium dicyanamide is a key parameter which supports the formation of highly (BMP-dca) and commercial silica nanoparticles (Ludox HS40) as ordered structures. The other factor is the a template. The N2 adsorption derived BET surface area of the meso-BMP is around 320 m2 g−1 and the total pore volume derived from NLDFT method is 0.749 cm3 g−1.80 NOMC with 2D hexagonal symmetry structure was synthesized via a facile solid–solid grinding/templating route, in which the ionic liquids (ILs) of 1-cyanoethyl-3-methylimidazolium chloride and SBA-15 were employed as the precursor and hard template, respectively. As-synthesized NOMC features with a uniform mesoporous size (3.5 nm), ropes-like morphology (0.4–1 µm in length) and high surface area (803 m2 g−1) with the nitrogen content of 5.5 at%.82 Mesoporous nitrogen doped carbon with surface area up to 325 m2 g−1 was produced through the nano hard template method using resorcinol, melamine, and formaldehyde as the carbon precursors catalyzed by the alkaline medium and mesoporous silica as a hard template.144- 147 It was believed that the nitrogen doping sometimes collapse the pore structure of the final porous carbons or creates a lot of defects. Stein et al. used an elegant approach in which a novel ionic liquid (IL) 1-ethyl-3-methylimidazolium dicyanoamide condensation/polymerization kinetics of intermolecular (EMI-DCA) based precursor which not only acts as a nitrogen precursor species. It has been realized that phenolic resins, source but also provides structural stabilization was used. In this nitrogen precursors, and polyethylene oxide (PEO)-containing approach, silica spheres were used as templates which block copolymers, which serve as the carbon sources and generated NOMC with a high specific surface area and a large structure directing soft templates, respectively, is considered as 2 −1 3 −1 81, 148, pore volume of 1393 m g and 4.5 cm g , respectively. the good combination for the direct self-assembly synthesis of 149 Ionic liquid based precursors are found to be the best NOMCs. For example, Liu et al. reported a one-pot route to sources for stabilising the porous structures of NOMC which prepare NOMCs having Ia3d and p6m symmetry with BET resulted a high specific pore volume owing to their good affinity surface areas in the range of 500 to 870 m2 g−1 in an aqueous 150-155 and adhesion on silica surfaces. media by dissolving the resorcinol, hexamethylenetetramine Most of these fabricated materials were made in the form (HMT) and Pluronic F127 into a dilute aqueous ammonia. It is of powder, which may not be useful for making devices for worth to mention that the symmetry of NOMCs changed from electrochemical sensing applications. Therefore, researchers Ia3d to P6m upon increasing of the carbonization temperature turned their attention to fabricate these NOMCs in a film form. and also by the simple introduction of trimethylbenzene (TMB) For instance, free-standing nitrogen-doped mesoporous carbon during the synthesis.83-85, 157 films were prepared by Peng et al. by carbonization of gelatin/HKUST-1 composite films, which were fabricated from gelatin/copper hydroxide nanostrands composite films. Gelatin provided the sources of both carbon and nitrogen whereas the copper hydroxides offered porosity. The formation of HKUST-1 crystals expanded the gelatin matrix and produced porous structures which were retained during the carbonization process.156

3.1.2 Soft templating approach As hard templating procedures requires the removal of the inorganic materials using toxic acids or strong bases, there has been a significant attention on the development of NOMCs using methods other than hard templating. Soft-templating is considered as one of the viable options to avoid this complex and toxic procedure involved in hard templating. In the soft- templating synthesis of NOMCs, two key issues should be kept in mind for the generation of ordered mesoporous frameworks. The first and the most important point to consider before using

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Direct synthesis of NOMCs with a high nitrogen content highly ordered mesoporous polymeric network (space group: through the soft templating approach remains a significant Im3̅m) with a high nitrogen content of 18 at% (Fig. 7A).94, 95 challenge due to the limited availability of nitrogen precursors Amino-acids based cooperative assembly route has been capable of co-polymerizing with phenolic resins without introduced by Liu et al. In this process, basic amino acids such deterioration of the order of mesostructural arrangement and as L-lysine and L-arginine, as polymerization catalysts, two a significant diminishment of nitrogen content during phenol derivatives, resorcinol and 3-aminophenol, were used as carbonization. Dai et al. reported on the direct synthesis of carbon and nitrogen sources and block copolymers F127 and NOMCs through the self-assembly of phenolic resins and a P123 as the soft templates. The NOMCs exhibited a BET surface Pluronic block copolymer via the soft-template method under area up to 256 m2 g−1 with cubic Im3m and hexagonal p6m pyrolysis of ammonia.86 This approach did not require any symmetry depends on the template used in the synthesis nitrogen-containing carbon precursors or post-treatment, but process.159 had the advantage of the preferential reaction and/or Yang et al. prepared nitrogen-doped carbon aerogels (NCAs) replacement of oxygen with nitrogen species, generated by by direct chemical synthesis by using an organic sol–gel process decomposition of ammonia at elevated temperatures, in with different mole ratio of tripolycyanamide (T) and resorcinol oxygen-rich polymers during pyrolysis. This method used (R). Then, the organic aerogels were pyrolyzed to obtain NCAs.

different steps including carbonization, nitrogen The N2 adsorption isotherms of the NCAs exhibit a typical type functionalization, and activation into a simple one step process IV isotherm with an obvious hysteresis loop at high relative and generated NOMCs with a uniform pore size, large surface pressure, which indicates that the prepared material has the area (up to 1400 m2 g−1), and a high nitrogen content (up to 9.3 mean pore diameter of 12.6 nm.160 The pore diameter of the at%). The nitrogen atoms are mostly bound in the form of NCAs was controlled by tuning the concentration of the N pyridinic and pyrrolic forms. precursors with a concomitant increase of the mesoporous Evaporation-induced self-assembly (EISA) process has also been tried for the preparation of NOMCs. Zhao et al. made tremendous contribution on the direct synthesis of NOMSc and established different methods for producing the same. Recently, this group has reported a controllable one-pot method to synthesize NOMC with a high N content up to 13.1 wt% by using F127, resol and dicyandiamide as a soft template, a carbon, and a nitrogen source, respectively. It was assumed that the resol molecules not only assisted the coordination of the template and the nitrogen precursors through a simple hydrogen bonding and electrostatic interactions but also provided the stability to the final ONMCs. The obtained NOMCs possess tunable mesostructures (p6m and Im3m symmetry) and pore size (3.1–17.6 nm), high surface areas of 494–586 m2 g−1.87 Later, NOMCs were prepared via a two-step approach by using resorcinol (R), formaldehyde (F) and dicyandiamide (DCD) mixture as the precursor. In this approach, dicyandiamide, formaldehyde and resorcinol were pre-polymerized in the

presence of Na2CO3 base catalyst to produce DCD-RF resol. The DCD-RF resol was mixed with a solution of triblock copolymer Pluronic F127 followed by the addition of 2 M aqueous HCl fraction. Mesoporous carbon aerogels with 0-4% nitrogen solution to facilitate the self-assembly and condensation in the content and surface area of 798 m2 g−1 were also prepared from 88-90 second step. Soluble precursors such as urea–phenol– 3D resorcinol (R) − melamine (M) − formaldehyde (F) aerogels formaldehyde resin has been used as nitrogen source for the by tuning the M/R ratio during the polymerization process.161 preparation of NOMC spheres with the mean diameter of 240 Dual soft templating technique, the combination of nm and Im3m symmetry through a simple co-assembly with the inorganic and organic template, has been recently receiving polymeric surfactants under highly acidic conditions (Fig. 7B). By much attention for the synthesis of NOMcs with tunable adjusting the ratio of urea to phenol, the nitrogen content of morphologies and pore diameters. Qiao et al. demonstrated the 91-93 the NOMCs was controlled. synthesis of a series of nitrogen-doped mesoporous carbon An aqueous cooperative assembly route has been also spheres (NMCs) synthesis via a facile dual soft-templating employed for the fabrication of NOMC with the body centred procedure using a resorcinol-formaldehyde resin and melamine cubic Im3m symmetry using resorcinol and as carbon and nitrogen precursors, and a mixture of Pluronic hexamethylenetetramine (HMT) precursors, copolymer F127 as F127 and Fluorocarbon (FC4) surfactants at different 158 soft template. Xue et al. and Choi et al. separately reported carbonization temperatures. The surface area (307-483 m2 g−1), on a co-assembly approach based on Pluronic F127 mediated pore volume (0.3-0.4 cm3 g−1), conductivity, and nitrogen- micelle to turn non-porous melamine and phenolic resin to a

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ARTICLE Journal Name doping (25-5.5 Wt%) concentration of the synthesized NMC aqueous base solution which had the specific surface area up to were tuned by adjusting the nitrogen content and pyrolysis 1159 m2 g−1 .100 Guo et al. demonstrated the preparation of temperature.99 Porogens combined with the Ni metal catalyst, nitrogen-doped mesoporous network-like carbon (NMNC) via melamine were added to control the graphitic nature and the hydrothermal reaction of glucose solution followed by pyrolysis porosity of the nitrogen doped porous graphitic carbon (NPGC) under ammonia atmosphere without using any external with a high surface area of 1027 m2 g−1 and a nitrogen content template. In this work, self-polymerization reaction of glucose of 7.7 wt%.96 On the other hand, Xia et al. used resol and molecules in aqueous solution occurred under hydrothermal dicyandiamide as the carbon and nitrogen precursor together conditions at 200oC. During this step, carbonaceous spheres with the porogen, TEOS to increase the specific surface area and were produced via aromatization and carbonization of glucose, the pore size of the NOMC to 1374 m2 g−1 and 7.4 nm, due to abundant functional groups (such as -OH, -CHO, -COOH, respectively.97 etc) on their surfaces. These spheres were colluded to form The polyhedraloligosilsesquioxanes (POSS) were also used colloidal network-like carbonaceous spheres through as carbon source and assembled into hierarchically porous intermolecular dehydration and cross-linking with the carbon structures by a block copolymer-assisted method using dehydration reaction among the carbonaceous spheres. The Pluronic P123 and F127 as the soft templates. The structure of obtained NMNC sample synthesized at 1000oC (NMNC-1000) the materials was tuned from hexagonal to cubic by changing exhibited extremely high specific surface area (2588 m2 g−1), the nature of the templates. The prepared NOMCs from POSS well defined spherical shape morphology and mesoporous exhibited the specific surface area of over 2000 m2 g−1 and a structure which are critical for mass transport and large pore volume of 1.19 cm3 g−1.162 Nitrogen-doped electrochemical applications.98 This elegant approach presents mesoporous carbon microfibers (NMCMFs) having surface area a unique way of improving the specific surface area and the of 230 m2 g−1 were prepared via an evaporation-induced tri- functional groups of the porous carbon materials. It can be consistent assembly of a triblock copolymer F127, resols and expected that different combinations of the carbon precursors prehydrolyzed tetraethoxysilane on natural silk followed by with inorganic metal or metal oxides will offer a new families of pyrolysis.163 Nitrogen-doped hollow mesoporous carbon porous carbon nanostructures. spheres (NHCSs) were also prepared from 2,4-dihydroxybenzoic acid and hexamethylenetetramine as precursors and a mixture 3.2 B doped ordered mesoporous carbons of Pluronic P123 and sodium oleate as a template, followed by Boron is one of the interesting element which can not only o thermal treatment at 650 C in ammonia atmosphere and change the electronic and electrical properties of the carbon o subsequent high temperature annealing at 800-1000 C in nanostructures but also the thermal stability under nitrogen or 102 nitrogen. Instead of POSS, TiO2 nanostructures were also air after the substitution in the graphitic framework. Boron- used as inorganic templates in order to ease the synthesis doped ordered mesoporous carbons (B-OMCs) were prepared process and obtaining the hierarchical micro/mesoporous using an in-situ approach via organic-inorganic co-assembly, in framework. Nitrogen-doped hierarchical micro/mesoporous which, boron-modified phenolic resins were used as the carbon carbon nets were fabricated via supramolecular assemblies of precursor, tetraethyl orthosilicate as the inorganic precursor block copolymer P123 with the assistance of dicyandiamide and and reverse amphiphilic triblock copolymer (PO97EO186PO97) as TiO2 nanostructures. The as-obtained carbon nets had the the soft template. B-OMCs with the BET surface areas of 1040 combination of both micro and mesopores that gave the to 1255 m2 g−1 and pore volume of 1.55 cm3 g−1 were also 2 −1 specific surface area of approximately 2144 m g and a high- prepared by co-impregnation and carbonization of sucrose and level nitrogen doping with a nitrogen content of approximately 4-hydroxyphenylboronic acid into SBA-15 silica template.103, 104 164 8.25 wt. EISA method has also been used for the preparation of B-OMCs Microwave technique which is considered as eco-friendly in which resorcinol and boric acid were used as the precursors and energy saving approach for the preparation of and Pluronic F127 as the soft template by combining the soft- nanomaterials has been used for the synthesis of NOMCs. Hung templating and hydrothermal techniques.106 The contents of et al. used this technique and prepared NOMCs with a high boron was easily tuned with a simple adjustment of the boric 2 −1 specific surface area (794 m g from carbon–silicate (C–Si) acid to resorcinol ratio. A dense, continuous and amorphous composites via co-condensation method using a melamine- boron-containing ordered mesoporous carbon (CB) films were formaldehyde resin oligomer as the precursor, and P123 also synthesized by using resols as a precursor for carbon, boric triblock copolymer surfactant and sodium silicate as the soft acid as a heteroatom precursor, and amphiphilic triblock 101 and hard template, respectively. Although the technique copolymer F127 as a template. In this case, evaporation- proposed was eco-friendly, it was found to be not suitable to induced triconstituent co-assembly method was used to obtain obtain NOMCs with excellent textural parameters which are highly uniform films which was found to have high chemical needed for enhancing the performance of these materials in inertness. This unique property of these films made them many applications including energy storage and conversion. attractive for corrosion resistance applications.105 NOMC with a cubic Im3m symmetry and rhombic 3.3 P doped ordered mesoporous carbons dodecahedral single-crystal morphology was also prepared via organic–organic self-assembly of triblock copolymer F127, 3- Phosphorus belongs to the group V in the periodic table and has aminophenol, and hexamethylenetetramine (HMTA) in the same number of valence electrons as nitrogen atom.

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SN-OMC material featured distinctive bimodal mesoporous structure with a high BET specific surface area ( 1100 m2 g−1) and uniform distribution of sulfur and nitrogen dopants.109 ∼ Different mixed precursors such as pyrole-sulfuric acid and polythiophene-polypyrrole (PPy) were also used for the preparation of SN-OMC which had well-ordered porous structure and tunable N and S contents.110 Instead of dual precursor, a single molecular precursor that contains both S and N was also used for the synthesis of SN-OMC. For example, SN- OMC were synthesized by nano-casting method using novel fluidic precursor – acrylonitrile telomer (ANT) and mesoporous silica SBA-15 as a hard template. SN-OMC contained both nitrogen and sulfur atom dopants with 4 and 0.6 at.% and also a high specific surface area of 1012 m2 g−1.165 One step nanocasting technique in which diphenylthiocarbazone was Although it has lower electronegativity than the N atoms, it used as a precursor for carbon, sulphur and nitrogen and SBA- exhibits almost similar chemical and electronic properties. 15 as a nano hard template was also developed for the synthesis However, phosphorous has a larger atomic radius and higher of SN-OMC.112 Sulfur-doped ordered mesoporous carbons electron releasing ability than nitrogen, which make it as an (OMC-S) with 1.5 wt% of sulphur and BET surface area up to excellent choice of dopant for carbon materials. Yu et al. 1261 m2 g−1 was prepared by using SBA-15 as the template and reported on the first synthesis of micron sized phosphorus- different amounts of sucrose and benzyl disulphide as the doped ordered mesoporous carbons (POMCs) with different carbon and sulfur sources, respectively (Fig. 9).113 lengths through nanocasting method using SBA-15 mesoporous

silica with different sizes, triphenylphosphine, and phenol as the 4.2 N and O co-doped ordered mesoporous carbons templates, phosphorus and carbon sources, respectively. The realized POMCs exhibited a high BET specific surface area of Polyamides have been used as precursors for the synthesis of 1182 m2 g−1, a large pore volume of 1.87 cm3 g−1 with a mean nitrogen- and oxygen- doped ordered mesoporous carbons pore diameter centred at 3.4 nm.107 The content of the P in (NOOMCs) by applying 3-aminobenzoic acid (MABA) and SBA- POMCs by tuning the amount of triphenylphosphine. The 15 mesoporous silica as a precursor and template through liquid amount of P in the carbon nanostructures also control the infiltration and thermal polymerization method. The obtained micropores in the samples. The specific surface area of the NOOMCs showed specific surface area up to 1084 m2 g−1 with a POMCs can be increased to 1338.8 m2 g−1 with a simple narrow pore size distributions and a mean pore diameter adjustment of the P content as it creates a lot of micropores in centred at 4.0 nm and nitrogen and oxygen contents as large as the walls (Fig. 8).108 Through a careful adjustment of the P in the 6 and 6.4–11.5 wt.%, respectively.166, 167 A mixture of molten synthesis mixture, porous carbons with different pore fructose and urea, which are low cost and environmentally friendly precursor, has also been used for the fabrication of Figure 10 (A) SEM image of Fe-N-GC-900. (B) EDS for Fe, N, C, cl and O. (C and D) Elemental mapping of Fe and N respectively. (E) The nitrogen adsorption- NOOMCs with 3D porous structure using mesoporous silica KIT- desorption isotherm of Fe-N-GC-900 and (F) Schematic illustration of the synthesis of micro and mesoporous Fe-N-GC with ordered structure. Reproduced with 6 as a template. The obtained NOOMCs exhibited enhanced permission from ref. 182. Copyright 2014, American Chemical society. surface polarity and a high specific surface area and pore 2 −1 3 −1 parameters and tunable electronic properties could be volume of 1197 m g and 1.16 cm g and heteroatom (O, N) obtained. contents of up to 19.1 wt.-%. However, the content of the dopants can be varied by tuning the quantity of the precursors.168 4. Binary atoms doped OMC 4.3 Ordered mesoporous carbons with B, P and/or N doping 4.1 N and S co-doped ordered mesoporous carbons The combination of P and B doping is another interesting dual Incorporation of dual heteroatoms in the OMCs provides unique dopant which afforded interesting structural and chemical chemical and electronic properties due to creation of defects properties. Hydrothermal doping strategy has been applied for and uneven charge distribution in the carbon framework the doping of boron and phosphorus into OMCs (HTBP) via a structure. This will also change the hydrophobic or hydrophilic facile aqueous self-assembly using resorcinol as the carbon nature of the surface of the framework. In this section, we will source, boric acid, and phosphoric acid as the heteroatom show the methods used for different types of OMCs with dual source. In this method, Pluronic F127 was employed as the soft heteroatoms dopants and their effect on the structure and template structure-directing agent. By varying the properties of the materials. Guan et al. reported sulfur and hydrothermal synthesis temperature, the concentration of B nitrogen doped ordered mesoporous carbons (SN-OMCs) by and P introduced in the OMCs can be controlled from 0.8 to 1.6 using SBA-15 as a scavenger under CVD conditions with the wt% and from 2.3 to 3.6 wt%, respectively.52 This was due to ferrocene, pyrimidine and thiophene precursors. After etching different interaction of B and P with C precursors at a high away the iron metal and SBA-15 silica template, the resulting

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ARTICLE Journal Name hydrothermal temperature. Triple hetero atom doping was also post-synthesis treatment either with NH3 or melamine over FDU carried on the OMCs. N, B, and P-doped ordered mesoporous type OMC materials.172 Pd supported on CMK-3 (Pd/CMK-3) and carbons with surface area up to 550 m2 g−1 were prepared by applying SBA-15 as a nano hard template, a mixture of aniline, triphenylborane and triphenylphosphine as precursors through nano templating approach.169 First nitrogen was introduced into the carbon matrix using aniline at 900 °C using Fe as a catalyst but the B and P atoms were incorporated into the N doped carbon matrix during the carbonization step.

4.4 Ordered mesoporous carbons with N and P doping N and P co-doped 3D cubic ordered mesoporous carbons (NP- OMC) with bimodal mesoporosity and surface area of 1968 m2 g−1 using saccharide as a carbon source along with urea and phytic acid (PA) as precursors for N, P and carbon, respectively, and cubic ordered Ia3d mesoporous silica KIT-6 as a hard template.170 2D N and P doped ordered mesoporous carbons (NP-OMCs) were also prepared by using sucrose, cyanamide and phosphoric acid mixtures and SBA-15 as the template. The prepared materials had a high BET surface area (1300 m2 g−1) and a large total pore volume of 1.64 cm3 g−1.171

5. Functionalised nanoporous carbon The functionalization of the porous structures with organic molecules or inorganic metal or metal oxide nanoparticles can introduce new properties to the parent materials. This will expand the application potential of the OMCs in various fields including adsorption, separation, sensing, energy storage and N-doped CMK-3 (Pd/N-CMK-3) materials were also prepared by conversion, and catalysis. The highly ordered porous structure impregnating CMK-3 powder with aqueous solutions of 1,10- with uniform pores and high specific surface area will provide phenanthroline and H2PdCl4 in two steps via ultrasound- enough space for the decoration of the surface with different assisted impregnation strategy followed by reduction using 30 o 173 functionalities which will enhance the properties that will be vol% H2/N2 carrier gas at 200 C. The N2 sorption analysis of helpful for various applications. However, the fabrication of Pd/CMK-3 and Pd/NCMK- 3 showed typical type IV isotherms these functionalities inside the mesochannels without any with clear hysteresis loops of H1-type, indicating that the agglomeration is quite challenging as the uniform distribution mesoporous structure and the relatively uniform mesopores of of these functionalities is the key to elevate the performance of CMK-3 were still preserved in Pd/CMK-3 and Pd/N-CMK-3 these materials in several specific applications. Several reports samples. Mesoporous carbon (MC-8) and nitrogen doped have been published in the literature on metal, metal oxides, mesoporous carbon (NMC-8) which were prepared by Zr-SBA- alloys, metal complexes, graphene, metal chalcogenides, and 15 as the template were also used as supports to get the Pd NPs amines or amine complexes, and proteins functionalized OMCs. of 4.0 and 2.5 nm. NMC-8 and MC-8 supports with surface areas In this section, we will highlight on the different methods used of 1054 m2 g−1 and 1489 m2 g−1 were prepared by carbonization for the immobilization of these functionalities in OMCs and how of mixture of xylene/furfuryl alcohol/oxalic acid with and these functionalities create new properties to the final without ammonia gas nitridation and the hard template materials. method using large pore Zr-SBA-15. Zr atoms were introduced into the template to obtain large pore size in the template 5.1 Metal nano particles immobilized nanoporous carbons which would be beneficial for the decoration of highly dispersed Pd nanoparticles which were prepared by wet-chemical Li et al. described the immobilization of ultra-small size Pd reduction method.174 nanoparticles (PdNPs) of 3.0 to 5.0 nm in size having uniform As the post-synthetic approach was considered as a time shape and without agglomeration in OMCs. In this method, consuming process, Ye et al. used a one-step co-calcination nitrogen doped OMCs was used in order to provide anchoring approach to prepare Pd NPs budded on NOMC (Pd/N-MCN) by support that would avoid the agglomeration of the small sized using phenol, formaldehyde, melamine, and PdCl2 as precursors PdNPs. The incorporation of PdNPs in the OMC-N was for C, N and Pd and F127 through soft templating method.175 In- performed in a two-step process, immobilization followed by situ synthesis approach was also adopted for the preparation of reduction using aqueous solution of NaBH4. The OMC-N of used Pd NPs supported on nitrogen doped mesoporous carbon in this study had 8.6 wt% of nitrogen which was introduced by

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(Pd/N-C) by direct pyrolysis of palladium dimethylglyoximate complex at 400oC under 10% hydrogen gas.176 However, the obtained Pd/N-c exhibited relatively low surface area and pore volume of 124.1 m2 g–1 0.158 cm3 g–1. An in-situ spray-drying method followed by the calcination route was used to fabricate the 3.8 to 4.5 nm sized Pt nanoparticles supported on nitrogen-

doped porous carbon microspheres (Pt/CN). This study showed that the size of the Pt NPs and N-doping into conventional carbon black were simultaneously controlled via spray-drying method and also by adjusting the precursor pH using ammonium hydroxide.177 Nano-Sn/mesoporous carbon parasitic composite was prepared by Duan et al. using 2+ immobilization of Sn solution and followed by H2 gas assisted reduction.178 Mesoporous carbon used to anchor Sn nano particles has an open porous structure with less than 10 nm filmy pore walls, and the pore diameter is about 30–70 nm,

which has been prepared using sucrose and CaCO3 template. The open porous structure of mesoporous carbon was highly favourable for the filling of tin nanoparticles of 10–30 nm which were uniformly distributed in the pores of carbon matrix. Cobalt and iron doped NOMCs (C−N−Co and C−N−Fe) with tunable nitrogen content (up to 9.5%) was prepared from direct carbonization of vitamin B12 and the polyaniline-Fe (PANI-Fe) Ordered hierarchically porous carbon co-doped with N and 179 complex, respectively and silica nanoparticles, SBA-15, and Fe (Fe-NOHPC) was prepared by Deng et al. through an EISA montmorillonite were used as templates. The specific surface process followed by carbonization under ammonia by using areas of these C−N−Co samples obtained by using the silica resol, F127 and FeSO4 as carbon precursor, soft template and nanoparticles, SBA-15, and montmorillonite were 568, 387, and iron source, respectively.184 Fe-NOHPC possessed N and Fe 2 −1 239 m g , respectively. These values were much higher than concentrations of 3.54 and 0.18 at%, with an ordered 2 −1 that of VB12/C (134 m g ). The mesopore size distributions of hierarchically porous structure, a high surface area (1172.5 m2 the above samples were centred at 12.0, 3.5, and 4.5 nm, g−1) and pore volume of 1.03 cm3 g−1. Ahn et al. reported on the 180 respectively, according to the BJH model. Mesoporous C-N- preparation of well dispersed Fe nanoparticles within N-doped Fe material was also prepared by using poly(4- vinylpyridine) mesoporous carbon nanofibers (Fe-NMCNF) with surface area 181 and iron chloride as the precursors and SBA-15 as a template. and pore volume up to 468.9 m2 g−1 and 0.95 cm3 g−1 from The mixture of metal and hetero atom doping provides polyacrylonitrile (PAN) and iron(II) phthalocyanine mixture much better chemical and electrical properties than that of 185 using electrospinning followed by reduction of H2 gas. OMCs doped with either heteroatom or metal nanoparticles. A Cobalt nano particles of 6.7 to 12.8 nm in size were series of Fe−Nx doped ordered hierarchically micro- and immobilized on the OMC-N materials through excessive mesoporous carbon (Fe−N−GC) materials were prepared wetness impregnation method using Co(NO3)2 precursor by through the nanomoulding synthesis procedures by direct auto reduction process without using any external reductant. pyrolysis of the various nitrogen containing heterocyclic The size of the Co nano particles was reduced from 12.8 to 6.7 compounds such as 2,2-bipyridine, p-aminotoluene, p- nm with an increase in the nitrogen content in the NOMC nitroaniline, and 2-amino pyridine, respectively, and iron samples from 5.8 to 10.4 wt%. However, the size of the particles chlorides in the confined mesoporous channels of SBA-15 (Fig. was increased to 19.4 nm when OMC without any N dopant was 182 2 10). Fe−N−GC had a high specific surface area of up to 929 m used, confirming the anchoring role of N functionalities in −1 2 g , which was composed of mesopore surface area of 499 m OMCs.186 Soft-templating method was also used for the in-situ −1 2 −1 g and micropore surface area of 430 m g , corresponding to preparation of Co nanoparticles in NOMCs. A 3D cobalt- their narrow mesopore size distributions centred at 6.3 nm and nitrogen-doped ordered macro-/mesoporous carbons (Co-N- micropore size centred at 0.37 nm. Li et al. used “task-specific” OMMCs) with 9.64 wt% of nitrogen and 1.52 wt% of Co were approach by using ferrocene-based ionic liquid [FcN][NTf2] (Fe- prepared from a mixture of resol/dicyandiamide IL) as a metal-containing feedstock with a nitrogen-enriched (DCDA)/Co(NO3)2 through a dual-templating approach using ionic liquid [MCNIm][N(CN)2] (N-IL) as a compatible nitrogen opal colloidal silica spheres as a macroporous mold and triblock content modulator and SBA-15 template to prepare copolymer Pluronic F127 as a mesoporous template. In the X 183 mesoporous iron-nitrogen-doped carbon (Fe @NOMC). synthesis process, an aqueous/ethanolic solution containing FeX@NOMC had a nitrogen content up to 11.9 wt% and highly resol, DCDA, Co(NO3)2·6H2O and F127 was infiltrated into the 2 ordered mesoporous structure, a high surface area (411–506 m void spaces of the silica opal template, and the mesostructure –1 3 –1 g ), pore volumes (0.71–1.05 cm g ) and pore size distribution was formed during an EISA process.187 The nitrogen was highly uniform centred at 5.6 nm. adsorption/desorption isotherms of Co-N-OMMCs samples

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ARTICLE Journal Name were of type IV with a high specific surface area and a total pore mesochannels of OMCs in order to reduce the total cost of these volume of 679 m2 g−1 and 1.71 cm3 g−1, respectively, with an catalytic systems. Wang et al. described the synthesis of PtCo average pore size centred at 11.2 nm. Direct polymerization of bimetallic nanoparticles with a molar ratio of Pt:Co of about a reverse copolymer PPO-PEO-PPO/[Ni(H2O)6](NO3)2/phenolic 1:1.1 supported on the NOMC framework with ultrafine resin self-assembled in ethanol medium yielded highly dispersion and uniform particle size distribution (ca. 1.5 nm) decorated Ni nanoparticles in the OMCs. During the pyrolysis through the wet impregnation method followed by the 2+ o 189 process, Ni was reduced into metallic Ni nanoparticle which reduction at 500 C in a flow of 5% H2 in Ar. The surface area, were uniformly distributed onto the surface of OMCs. pore volume and pore size of PtCo/NOMC were 507 m2 g−1, 0.41 cm3 g–1 and 6.5 nm, respectively. NiFe alloy nanoparticle 5.2 Alloy nano particles incorporated nanoporous carbons encapsulated in mesoporous nitrogen-doped carbon sphere The combination of metals can introduce unique electrical and (MNCS) were also synthesized using direct thermal pyrolysis of o electronic properties as it tunes the electronic structure of the nickel hexacyanoferrate at 500 C without using any external 190 nanoparticles. In addition, the alloy system has also been template (Fig. 11). Pd3Cu alloy nanoparticles were also employed in many catalytic systems owing to their ability to encapsulated inside the mesochannels of NOMCs using PdCl2 lower the activation barrier system. Most importantly, the and cupric acetate as precursors for Pd and Cu, and sodium 191 concept of alloying can also significantly reduce the cost of the citrate as a reducing agent via wet chemistry method. materials. By decorating these alloys system on highly ordered support system, the active specific surface area or the 5.3 Metal oxides and metal chalcogenides functionalized nanoporous carbons Metal oxide nanoparticles have been widely used in various applications. However, the textural properties of these oxides are the limiting factors which affect the final performance of the materials in different applications. On the other hand, metal chalcogenides are unique semiconducting materials and they complement semi metallic graphene. They are widely employed in electronic and optoelectronic applications owing to their small energy band gap. By functionalizing these metal chalcogenide or metal oxides nanostructures inside the mesochannels of OMCs, new advanced porous materials with improved properties can be realized. Shen et al. reported on

the synthesis of mesoporous Li4Ti5O12/C nanocomposite by post functionalization of acid treated CMK-3 through the sintering of lithium acetate and tetra butyl titanate precursors at 750°C for 192 6 h in a nitrogen atmosphere. The small Li4Ti5O11 nanocrystals were nicely interconnected in the mesochannels of OMCs which significantly increased the ionic and electronic conductivity of the composite system. These factors are critical for energy storage applications, especially in battery. A significant reduction of the specific surface area from 1138 m2 g−1 to 127 2 −1 m g confirmed the formation of these Li4Ti5O12 nanocrystals inside the mesochannels of the OMCs.

Meso-porous C–TiO2 nanocomposites with anatase TiO2 whose contents ranging from 40wt% to 87wt was prepared

through EISA strategy by using TiCl4 and/or Ti(OC4H9)4 as titanium sources, phenolic resin as the carbon source, and properties of the alloy nanoparticles can be significantly altered. triblock copolymer F127 or P123 as the structure-direct 193 In this section, we will summarise different methods employed agent. Nitrogen-doped urchin-like Fe3O4@C-N composites for the fabrication of various alloys or bimetallic doped OMCs were prepared by a simple hydrothermal carbonization of and how these nanoparticles affect the properties and of the hydroxyferric oxide (α-FeOOH) coated with polydopamine final materials. (PDA) at 400 °C under Ar atmosphere.194 Cobalt oxide particles Maiyalagan et al. reported on the deposition of Pt-Ru alloy of 30-50 nm encapsulated in nitrogen co-doped carbon (Co– nanoparticles of 3.8 nm size with atomic ratio Pt/Ru (1:1) and N/C) bi-catalysts were prepared via a one-pot approach by using 20 wt% of metal loading (Pt-Ru) in the highly ordered dopamine hydrochloride (DA) and formaldehyde (F) as a mesoporous carbon CMK-8 by using sodium borohydride based nitrogen containing carbon sources, P123 as a soft template and 195 wet chemical reduction method.188 The noble metals were co- cobalt acetate as a precursor for Co. Iron sulphides (Fe1-xS) doped with transition metal nanoparticles inside the embedded in nitrogen and sulfur dual-doped mesoporous

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graphitic carbon spheres (Fe1-xS/N, S-MGCSs) were synthesized Porous and non-porous carbon nanofibers (PCNF and CNF) via a two-step pyrolysis followed by acid leaching process. The were prepared and used as spacers to synthesise high surface 199 preparation of Fe1-xS/N, S-MGCSs involved the coordination of area 2D graphene (G) prepared at 900 ˚C. In the typical Fe2+ with PDA followed by carbonization and leaching of iron synthesis, graphite powder was chemically modified through oxides and finally vulcanization under thiourea. The prepared acidification in two steps to get oxidized graphite and on

Fe1-xS/N, S-MGCS materials had the specific surface area and exfoliation and lyophilisation through ultra-sonication process, pore volume up to 371.4 m2 g−1 and 0.41 cm3 g–1, respectively.196 the graphene oxide (GO) powder was obtained. The resulted GO

N-doped mesoporous carbon capped with MoO2 nanobelts (MoO2@NC), a core–shell-structured nanocomposite comprising a MoO2 nanobelts core and an N-doped mesoporous carbon shell was prepared by in situ thermal reduction of MoO3 nanobelts, accompanied with the N-doped carbon from the polypyrrole precursor via one-step annealing process.197 Sun et al. described a facile melt−impregnation method for the

confinement of Se2S6 ultra small nano crystals into the nitrogen- 198 doped mesoporous carbons (Se2S6/NMCs). In the synthesis of Se2S6/NMCs, selenium and sulphur melts are miscible with each other at 500°C and then infiltrated into the mesopores of NMCs.

The composite Se2S6/NMCs had a considerable amount of mesoporosity with a specific surface area of 159 m2 g−1 and pore volume of 0.8 cm3 g−1.

5.4 Graphene functionalised nanoporous carbon Graphene, a two-dimensional form of carbon layers with crystalline honeycomb lattice and their layers are connected by relatively weak forces, has received substantial importance due to the open porous structure accrued from the stacking. This typical behaviour of graphene tends to exhibit exclusive physical and chemical properties due to its ease in stacking to form graphite and can be rolled to form nanotubes or spherical fullerenes. Although graphene is a fascinating material with an effective surface area, the undeveloped porous structure limits the opportunity in developing the graphene into useful multi- dimensional flexible materials. Recently, various constructive ideas have been executed to build the graphene with nanoporous structures and to utilize their surface defects originated from imperfections of the crystal lattice, for immobilisations and anchoring various nanoparticles or by fabricating hybrid graphene materials. Noteworthy, the powder was mixed with the PCNF and CNF to obtain G-PCNF and chemically synthesised graphene through coupling reactions G-CNF. The 2D graphene sheets were further functionalised by are usually said to be nanographene and nanoporous graphene Pt to form Pt/G-PCNF and Pt/GNF through magnetic stirring and which is the hot topic in the development of new generation the Pt was reduced by refluxing, following the polyol reduction materials. method. The difference between the porous and non-porous 2D Despite of graphene being one of the highest surface area graphene materials were demonstrated through the FESEM, materials, the graphene derived materials pronounce a very low where the G/PCNF showed mesoporous structure and the surface area when compared with the single layer graphene rough surface of the porous material provided more active sites especially due to the π stacking exhibited by the graphene for the catalyst deposition. Like spacers, other bridging sheets. Therefore, it is wise to implement porosity on the molecules were also used to bridge the graphene sheets. For graphene based materials to increase the specific surface area example, the synthesis of porous carbon nanosheets by using and so far, there are four effective ways to do the purpose asparagine, which is an amino acid and used as a bridging namely: exfoliation technique, templating methods, molecule to connect the GO and the electrostatically connected stacking/aggregation and reduction of graphene oxide to form GO served as the structure directing agent to form porous core or hydrogels and finally integrating graphene using nanosheets was reported.200 The GO was also exfoliated into spacers. In this section, we will focus on the functionalization of discrete sheets through ultrasound and the individual sheets graphene on the mesoporous channels of OMCs. were then converted into 3D graphene composite (GN) by depositing Au nanoparticles and reduced by using PEG. Thus,

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ARTICLE Journal Name prepared 3D-AuNPsGN increased the active surface area for better electrochemical performance compared to that of pure electrochemical sensing of the antibodies.201 CNT/graphene.206 The specific surface area was lower and the It is well known that, the multilayer graphene (MLG) has porous structure of the coated CNT was not controlled through higher mechanical strength and at the same time, has lesser this method. In comparison to this study, the eminent ordered properties compared to that of single layer graphene. With the porous carbon prepared from SiO2 colloidal crystals was objective of allowing wide range applications of MLGs, the MLG reported as a better spacer by Fei et al. and fabricated GN/PC was combined with porous carbon (PC) through CVD process to aerogel. Their fabrication process involved the ultra-sonication form hybrid MLG/PC core shell films, where their structure was of the PC and graphene oxide (GO) suspensions and after controlled by nickel gauze which was used as the template and hydrothermal process at 180 ˚C, graphene/porous carbon their pore sizes were controlled by the CVD reaction time and hydrogels were obtained. Interestingly these aerogels exhibited tuning the methane feeding rate. Since the hybrid MLG has the enhanced rate performance when compared with the individual characteristics of graphene and porous carbon, the film could GN and PC.66 Similar to the previous report, the pore structure maintain the structure that fetched a huge advantage of the graphene materials was simply controlled by assembling containing MLG shell and PC core, with the nanoporous.59 PC the graphene into three-dimensional structure by hydrothermal have shown tremendous advantage owing to their excellent treatment. The agglomeration of the colloidal GO suspension structural and textural properties and ones again porous carbon after 150 ˚C resulted in hydrogel and dried, to assimilate the microspheres (PCs) in combination with graphene to forge sulphur. The bounded sulphur was uniformly anchored to the hybrid film was reported by Hongbo et al.202 They followed graphene sheets. The porous structure thus produced was used three conventional steps namely reduction, leavening and as a model to study the influence of pores on electrochemical compression to fabricate the hybrid flexible porous film. The performances.207 The graphene treated with PC was also doped porous carbon microspheres moved between the pore walls of with nitrogen and activated by adding KOH via insitu the flexible graphene nano sheet (GNS), prevented the stacking polymerisation and was used as an anode.208 N-doping was also of the GNS and kept the open porous system in confinement done through insitu carbonisation technique where glucose was facilitating electrochemical performance. mixed with GO to form RGO-HTC carbon in large scale and was

Although porous carbons are fascinating, they relatively activated using NH3 to form nano-sandwich N-doped carbon have poor electrical conductivity. For example, CMK-3 has a materials (NNCMs)209 as shown in Fig. 13. Among the various poor electrical conductivity and cyclability compared to the NNCMs synthesised at 850, 900, 950 and 1050 °C, NNCMs graphene. To combine the bright side of porous carbon (CMK- prepared at 1050 °C exhibited a high surface about 1959 m2 g−1. 3) and graphene, in 2015 Nan et al. synthesised graphene based 2D porous carbon which was used as a support for the 5.5 Fullerene based porous carbons 203 functionalization of Pt nanoparticles. In the following year, Fullerenes are the purest forms of carbons connected by strong the same group has demonstrated the functionalization of hexagonal and pentagonal rings, where their structure differs graphene based mesoporous carbon with Pd and SnO2 from varieties of fullerenes based on their 5 and 6 ring units. nanoparticles as shown in Fig. 12. They used the SBA-15 silica The major difference between the graphene and fullerene is template and graphene to prepare graphene mesoporous that, the fullerenes have a very high thermal and mechanical 204 carbon (G-mc). By following the electroless plating method, stability but have a very poor surface area and electrical Pd/SnO2 were introduced to the G-mC to form G-mC-Pd/SnO2. conductivity. Controversial to fullerenes, graphene has a very Thus, metal functionalised porous graphene exhibited decrease poor stability but has a high surface area and high electrical in the surface area and pore volume, suggesting that the conductivity. However, the high symmetrical structure of Pd/SnO2 were located inside the pores of G-mC. This was fullerenes is unique compared to any other existing carbon confirmed by TEM images that show only a few large Pd and materials so far, that provides opportunities to the scientific SnO2 nanoparticles found outside the surface of CMK-3. It was world to explore their structural properties for various found that the particle size of the G-mC was close to the particle applications. At the same time, the rigid structure of fullerenes size of the Pd/SnO2 nanoparticles and was conductive could only be modified organically but due to its high thermal compared to the CMK-3-Pd/SnO2. and mechanical stability it is not very easy to be fabricated into Graphene oxide was also coated on the polyacrylonitrile nanoporous fullerene structures. The rare reports on fullerene derived porous carbon (PAN) that is rich in nitrogen and oxygen nanoporous carbons are discussed in this session. species. By heating the coated PAN (PAN/GO) followed by Considering the effect of templating methods, Duncan et al. activation and washing with acid produced the final product. tried to self-assemble the fullerene by immobilising the The oxygen present in the final product inhibited the graphene fullerenes on the graphite surface, where the pores were layer stacking and provided strong interactions between the generated by 1,3,5-benzenetricarboxylic acid to form fullerene 205 sheets. A simplified strategy of synthesising graphene/porous monolayer.210 Inspired by the concept of self-assembling carbon was reported earlier in 2015, where the CNT was coated process, the single crystal C60 (FNR) and single crystal C60- with activated porous carbon (CNT@AC) and was used as nanotubes (FNT) were synthesised through liquid-liquid spacers dispatched in-between the graphene sheets interfacial precipitation technique. These nanostructures can (RGO/CNT@AC). The coated CNTs played a vital role in be transformed into nanoporous carbon (HT-FNR and HT-FNT) inhibiting the restacking of the graphene layers displaying a

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5.6 Amine functionalised nanoporous carbon

with random graphitic nature after the high temperature and Nanoporous carbons are unique due to its high surface area, pressure treatment. Finally, to understand the structural large pore volume with highly ordered porous structure. transformation, theoretical calculations were applied. It was Regardless of their excellent features, they limit themselves proved that high temperatures and pressures favor the from surface-active sites due to their hydrophobic nature. The formation and breaking of the interfullerene bonds which is the lack of active sites highly hinders the materials from various key for the transformation of 0D fullerene nanostructures into applications like sensing, separation, physisorption and 2D graphitic nanostructures.211 The exfoliated graphite was chemisorption, catalysis, etc. The hydrophobicity of these carbons can be tuned by functionalisation, especially with used as a carbon adsorbent and the polycrystalline C60 powder was mixed along to be adsorbed by the exfoliated graphite. The organic groups rather than using metal or metal oxides for functionalisation. In the below session, the functionalization adsorbed C60 on thermal treatment evaporated and the remaining particles were cold pressed.212 The porous carbon, using amines are discussed, since amines have relatively a high based on fullerene and graphite was studied for electrical, affinity to bond with carbon. So far, two main strategies such as optical and various other properties. One step further in the grafting and impregnation have been adopted for introducing development of fullerene based porous carbon, Tan et al.213 amines to the porous materials. activated the fullerene using KOH and doped the fullerene CMK-3 was functionalised by more than one amine groups likely 1,2-diaminopropane, trans-1,2-diaminocyclohexane and based porous carbon by nitrogen to form N-aC60 through o thermal annealing as shown in Fig.14. Interestingly the surface -phenylenediamine through C˗N cross coupling reaction. The area of the activated fullerene based porous carbon was 1457 aliphatic, cyclic and aromatic amines formed amide bonds on m2 g−1 while the N-doped fullerene based porous carbon was the surface of the CMK-3 material offering the catalytic sites to 1274 m2 g−1. The nanoporous fullerene is a new area and the produce carbonyl compounds, without any destruction to the 215 discussion on the fullerene based porous carbon signifies that a long-range ordering of the CMK-3 material. To increase the et al. wide knowledge is necessary to understand the bonding nature heterogenicity of the carbon, Zakova used five different between the self-assembled fullerenes and the interactions sources of amine to work on amine-amide combinations. The between the porous fullerenes and various other factors like carbon nanoparticles (CNP) were modified with amides to

polymerisation, ordered porous structures are yet unknown. manifest COOH groups and refluxed with SOCl2 to yield -COCl 216 Very recently, a striking report by Vinu et al. proved the groups to start the reaction of CNP with amines. Although the successful fabrication of highly ordered mesoporous fullerene XPS and Raman spectra confirmed the modification of the CNP (Fig. 14 B), with crystalline walls for the first time. The prepared surface with the expected bonding, the N2 adsorption- material showed excellent energy storage and conversion desorption showed a tremendous decrease in the surface area 217 properties. This discovery is going to make a huge impact in the after the grafting process. Amine grafting was also carried out 218 field of fullerene. We believe that this research would attract in porous polymeric networks, carbonaceous 219 220 many researchers to work in this new area of research as they nanomaterials, porous carbon monoliths and MCM-41. would be useful for a wide range of applications in the near Among these amine functionalised materials, MCM-41 future.214 invigorated with carbon nanoparticles fetched bimodal porous structure to the resultant amine functionalised MCM-41 carbon

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ARTICLE Journal Name material. The advantage of the bimodal porous structure on centuries and various methods have been developed to serve amine functionalisation is the increase in the adsorption the purpose. However, to best describe the approaches phenomena.221 The trendy way of fabricating amine adopted so far to immobilise the proteins can be split into three functionalised porous polymer222 and organic polymers223 categories, they are immobilisation through covalent bonds, which did not require any activation process was also reported. non-covalent bonds which includes hydrogen bonds, However, the cost was comparatively higher that limits the electrostatic and van der Waals interactions and finally through large-scale production. encapsulation. The immobilisation can also be described as adsorption process where a molecule can be entrapped or 5.7 Nanoporous carbon with metal nanoparticles from metal adsorbed on to a support through the three types of complexes interactions said above. Metal complexes, generally known as coordination compounds The nanoporous carbon can serve as an excellent substrate 230, 231 are complexes that form intermolecular bonds between the for the immobilisation of proteins owing to its high surface metal acting as an electron accepter and ligand acting as an area, narrow pore size distribution and tuneable pore sizes that electron donor. The ligands are also termed as mono, di, tri, or can be suitable for the proteins to entangle into the pores. poly-dentate depending on the number of electron it donates. Moreover, the hydrophobicity of the nanoporous carbon For instance, if the ligand donates more than one pair of protects the immobilised protein from solubility and various electron, the bonding between the metal ion and the ligand will other factors like mechanical and thermal instability and can 232 be more stable. The ability of the porous carbons to allow the even cease the denaturation of proteins. The commercially accessibility of small ions or metals due to their open channels available microporous carbon with small mesopores (Norit DLC make them as excellent candidates to fabricate nanoporous super 50) was investigated for adsorption of angiotensin 233 carbons with metal complexes.224 converting enzyme (ACE) to inhibit the peptides and food 234 Copper(II) acetate225 and copper(II) /silver(I) carboxylates protein and was monitored through the N2 adsorption were immobilised in the nanoporous carbons and their desorption process. Likewise, two different types of aprotinin combination was used to study the dihydrogen complexion.226 namely bovine serum albumin and bovine pancreatic trypsin Foley et al. also reported the preparation of simple complexes inhibitor was adsorbed in an open structured hydrophobic of copper and silver loaded nanoporous carbon which showed carbon aerogel (C1) consisting of mesopores and their highly selective adsorption of 1- 3 mol of hydrogen per metal adsorption capacity was compared with the commercially center. It was assumed that the cooperative interactions available hydrophilic nanoporous carbon (C2) having higher between hydrogen, the nanoporous structure, and the highly surface area than C1. Interestingly, the C1 exhibited the highest dispersed metal centers of the complexes in the mesochannels adsorption capacity for both the proteins. This clearly shows supported the enhancement of the hydrogen adsorption.225 It that the mesoporous carbon has a superior capacity over other was also reported that highly ordered nanoporous carbons with porous carbons due to their pore size and allows the migration metal nanoparticles were prepared through a simple of the proteins inside the porous channels due to the carbonization of magnesium polyacrylate complex227 and hydrophobic nature of the carbon compared with the benzoate metal complexes228 and exhibited a high specific commercially available hydrophilic carbon which tends to the 235, 236 surface area of ca 1050 m2/g. However, the surface area of the agglomeration of proteins. materials was significantly enhanced (1466.4 m2 g−1) when the Apart from immobilisation, proteins were also used as a 237, 238 composite was activated using KOH. By using the same carbon precursors to fabricate 3D porous carbon and carbonisation method, the cobalt ion absorbed polyaniline activated nanoporous carbon with high surface area and 239 (PANI) was converted into Co-C-N complex, which showed functionalised with organic groups like sulphur or metal 240 excellent electrocatalytic activity.73 The metal complex derived oxides like MnO2 to impose electrical conductivity. Since the porous carbon was also functionalised with selenium and the proteins can denature easily by physical environment like pH, selenium interacted to the metal complex porous framework high temperature and acidic conditions, instead of proteins through Se-O and C-O bond.94 being used as carbon source, alternatively protein themselves were used as templates to fabricate mesoporous nanocrystals 5.8 Protein functionalised nanoporous carbon as shown in Fig. 15, wherein the mesoporous NaTiO2 (MNTP NC) was coated with BSA and was dispersed in the oxidised Biomolecules are organic molecules derived from living tissues multiwalled carbon nanotube solution (MWCNTs). Finally, the composed mainly of carbon and hydrogen. Among the four class MWCNT and MNTP NC were assembled through electrostatic of biomolecules namely carbohydrates, proteins, lipids and interaction and thermally annealed to form MNTP/MWCNT nucleic acids, the proteins are of great interest due to their film.241 This film exhibited surface area of only 88.7 m2 g−1 with polymeric structure since they are the natural heteropolymers the typical type IV isotherm and they were analysed to be containing carboxyl group and amino group connected by composed of 63 wt% MNTP and 30 wt% MWCNT. peptide bonds. But, the common drawback of protein is its In another report, the interaction of plasma or the blood 229 denaturation, physical instability and side reactions caused proteins with graphitic carbon modified SBA-15 were also by the hydrogen bonds. Therefore, the importance of trapping investigated and concluded that the graphitic domains the proteins for useful applications has been realized since influence the interactions of complex protein-nanoparticle.242

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From the above reports on protein assisted templating interaction between the surface functional groups of methods, it could be noticed that the bare protein needs a nanoporous carbon and the ammonia caused the protonation + templating substrate which otherwise would collapse the of NH3 to NH4 that resulted in the electrochemical protein. Moreover, the proteins being used as a carbon performance towards gas sensing.247 Travlou et al. also precursor also have the major drawback of denaturation during demonstrated a series of the toxic gas sensing and have carbonisation process. As an alternate way, hydrothermal summarised the role of oxidation to examine the -N and -O method was employed to carbonise egg-protein using graphene heteroatoms on the nanoporous carbon surface and the effect nanosheets which play the role of template as well as catalyst. of pores contributing to the electrochemical responses at By this method, the protein can be avoided from any physical or different ammonia concentration and further studied the chemical damage through the strong bonding between the GO selectivity of sensor by exposing the carbons at oxidized state 248 249 and protein, which was further activated using KOH to yield to the H2S. The sensing of heavy metal ions and toxic heteroatom doped highly porous carbon material.243 chemical like hydrogen peroxide250 was also done by using nitrogen doped porous carbon and nanoporous carbon fibres. The ordered nanoporous carbon was also fabricated in film 6. Applications of functionalized nanoporous forms by Jia et al. who were successful in creating a high surface carbon materials area with tunable the pore sizes. These porous films exhibited an enough space for the immobilisation of glucose oxidase that As nanoporous carbons with different functional groups can exhibited an excellent bio sensing performance at a detection offer interesting chemical and physical properties, these limit of 1.5 mM,251 as shown in Fig. 16. The nanoporous carbon materials were effectively utilized for various applications.150, films with nickel for selectively sensing glucose was also 244, 245 Many investigations have focused on the usage of demonstrated.252 Nanoporous carbon was also functionalized functionalized nanoporous carbon materials for a range of with copper to have an active surface area that showed potential applications including conventional Li-ion and post Li enhanced sensitivity for the detection of biochemicals.253 batteries, supercapacitors, electrocatalysts for oxygen Nanoporous carbons were also employed as sensors for reduction reaction (ORR), fuel cell supports, hydrogen storage, selectively detecting various biomolecules like DNA bases, acids CO2 capture and field emission properties. This is mainly due to like ascorbic acid, uric acid, and NADH.254, 255 the fact that these fascinating materials can offer highly ordered

porous structures, high specific surface areas, large pore 6.2 Nanoporous carbon for drug delivery volumes and a uniform pore size distribution. In this section, we will address the importance of the functionalization of The effective drug carrier/drug vehicle is the most demanding nanoporous carbons and how these functionalities and component in drug delivery applications. The addition of the excellent properties can elevate the application possibilities in specific targeting in the drug delivery system is also an various fields. important factor for deciding on the efficacy of the drug delivery system. There are many carriers like nanoporous silica, 6.1 Nanoporous carbon for sensing polymers, micelles, nanotubes, nanoporous carbon etc have been employed for this purpose. However, the biocompatibility The application of carbon based materials for sensing has been of these materials is still under research and recently the widely studied and the demand for selective sensing are nanoporous carbon or the functionalised nanoporous carbons changing day-by-day for various reasons including are of interest in the field of drug delivery. environmental monitoring and safety, medical diagnostics etc. Clarithromycin, a drug normally used for the treatment of Majority of the sensing materials exhibit a high sensitivity, but tonsillitis, sinusitis and pharyngitis, causes side effects like high selectivity is the key and a new component that is now swelling of mucosal tissues. In order to reduce the side effects added as a trend to the sensing materials. The non-porous of clarithromycin, the nanoporous carbon functionalised with materials like graphene, carbon nanotubes and porous amine groups was used as a carrier molecule (Fig. 17). It was materials like activated carbon etc fall under the high sensitivity reported that the amine modified nanoporous carbon was materials. On the other hand, the functionalized nanoporous completely biocompatible.256 The nanoporous carbon derived materials can offer both high sensitivity and selectivity towards from MOF was also examined through cytotoxicity assay and sensing which is discussed below. the narrow pore size distribution was found to be suitable for The nanoporous carbon can be used for selective sensing by the controlled release of cisplatin.257 The dissolution and the various methodologies like functionalising NC with metal or poor solubility of the valsartan drug in the water was also metal oxide, surface modification and doping, to sense the toxic addressed by Zhang et al. who used the porous carbon gases, heavy metals, biomolecules etc. The selective sensing of monoliths possessing ordered macropores and uniform NH3 gas was performed by heteroatom doping by Travlou et al. mesopores of about 5.2 nm as a drug career.258 It has been where the interaction of NH3 with humidity (H2O) played a reported that the material exhibited a higher release rate major role in sensing through hydrogen bonding and transport compared with the pure valsartan. of proton through ionic conductivity.246 The similar sensing

mechanism was followed to sense NH3 gas using the polymer derived nanoporous carbon. It was found that the weak

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carbons and Leticia et al, reported on the conversion of oxidized surface to exhibit chemical reaction in the porous matrix and studied the photochemical response.261

6.3 Nanoporous carbon for catalysis

The increasing demand in the consumption of fossil fuels has 6.4 Nanoporous carbon in adsorption and separation almost depleted the fossil fuel sources, hence the renewable energy must be found and developed to save the environmental Adsorption is the most conventional application of nanoporous pollution caused by the fossil fuels and to mitigate greenhouse carbon compared to various other applications of nanoporous gasses. As an alternate source, many renewable energy sources carbon owing to their high surface area and tunable and are emerging and being developed with the aim of replacing the uniform pore size distribution. Despite of the advantage of the depleting sources. Among them, the hydrogen fuel is a nanoporosity, apparently, purification process which is blooming area in catalysis due to its non-toxic nature, fast otherwise said separation remains to be a difficult task so far. recharging ability and high stability. To produce the hydrogen, Hence, there is a clear need of developing advanced two well-known pathways have been used namely, the nanostructures for the efficient adsorption and separation dehydrogenation and dehydration. However, the later pathway applications. gives out the toxic carbon monoxide (CO), which is highly The neonicotinoid insecticides was extracted from water dangerous to the environment and immense control should be and fatmelon samples by the magnetic MOF derived 262 taken during the production of hydrogen. The main problem nanoporous carbon reported by Hao et al. In their typical persisting in the field of catalysis is the separation of the product synthesis, the magnetic nanoporous carbon was prepared by and their reusability. Hence, it is necessary to fabricate efficient one step direct carbonisation of ZIF-67 and the embedded Co heterogeneous catalysts which is highly cooperative with nanoparticles offered the magnetic property to the material reaction temperature and the PH of reaction medium is which could demonstrate the adsorption and removal of desirable in recent years. insecticide through liquid chromatography. Mesoporous carbon The synthesis of nanoporous carbon deposited with Pd derived from MOF was also reported later for the separation of 263 nanoparticles to synthesise the heterogeneous catalyst with the CO2 and CH4 from the mixture. On the other hand, the strategy of sodium hydroxide assisted reduction was reported magnetic mesoporous carbon (Ni-CMK-3) was also reported for 264 by Zhu et al. The sodium hydroxide was used here for the reason the adsorption and removal of sulfur from oil and the pure 2 −1 of uniform dispersion of metal on the surface of the nanoporous CMK-3 with a high surface area of 1268 m g was employed carbon and the reduction assisted by the sodium hydroxide for the adsorption and recovery of 2-phenylethanol which is a 265 resulted in the generation of hydrogen from the formic acid rose oil component. Following the use of mesoporous carbon decomposition without the CO side reaction. Interestingly, the in adsorption and separation, Ma et al. functionalised turn over frequency (TOF) was also 2623 h-1 with a 100% nanoporous carbon with highly uniform MgO nanoparticles hydrogen selectivity,259 shown in Fig. 18. The N-doped through EISA process for the separation of methanol. The 266 nanoporous carbon was also surface functionalised with AgPd largest adsorption capacity of 11.90 mmol/g was observed. zeolite framework for the decomposition of formic acid and the Perreault et al. functionalised and grafted mesoporous carbon 1 TOF reported was 936 h-1 at 353 K.260 These two reports clearly with diglycolyl chloride (DGCI) and N, N -bis-chloropropyl showed the advantage of nanoporous carbon over the zeolite diglycolamide (CI-PDGA) to form CMK-8-DGO and CMK-8-PDGA. framework decorated with nanoporous carbon. Oxidation had These two grafted CMK-3 materials were used as adsorbents to a key role in the surface modification of the nanoporous study the adsorption of lanthanides. Although both the

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Shen et al. have used mesoporous Li4Ti5O12/C nanocomposites as an anode material in Li ion battery. Cyclic

voltammetry curve of the mesoporous Li4Ti5O12/C electrode at a scan rate of 0.2 mV s−1, at a potential window of 1.0–2.5 V (vs. Li/Li+) showed a pair of well-defined redox peaks at 1.65/1.50 V, which was attributed to the redox reaction of Ti4+/Ti3+, respectively.192 These features revealed that the nanocomposite electrode had fast lithium ion insertion and extraction kinetics that was attributed to the highly ordered mesoporous structure with an enhanced electrical conductivity.

Li4Ti5O12/C nanocomposite possessed superior cyclic stability performance of more than 1000 cycles at the discharge capacity of 103.1 mAh g−1 at a high rate of 20 C with only 5.6% capacity loss (Fig. 20 e-f). Tan et al. reported that the N-doped

mesoporous carbon-capped MoO2 nanobelts (MoO2@NC) electrode delivered a high first-cycle discharge and charge capacities of 942.3 and 690.7 mAh g−1, respectively, with a Coulombic efficiency (CE) of 73.3 %. In the second cycle, the CE of the anode sample increased to 94.6 %, indicating a good components showed type IV isotherm, at lower pH the CMK-8- lithium ion insertion/extraction performance during the cycling 267 DGO exhibited excellent reusability of Ln(Fig. 19). process. The discharge capacity MoO2@NC electrode remained An interesting report on the effect of different pore at 692.4 mAh g−1 after 100 cycles at a current of 0.5 A g−1.197

structures in the adsorption and separation of CO2 from the Sun et al. also demonstrated that the Se2S6/NMC electrode mixture of CO2 and hydrogen was presented by Kumar et al. The exhibited the initial discharge capacity of 1195 mAh g−1, which molecular stimulation studies clearly showed that the was almost close value to the theoretical capacity of 1226 mAh −1 adsorption is and separation was quite sensitive to pore g for Se2S6. They also registered excellent cycle stability and a structure and the composition of nanoporous carbon high initial Coulombic efficiency of 96.5% as well as a high nanostructures. It was found that the porous carbons with tube reversible capacity of 883 mAh g−1 after 100 cycles and 780 mAh like structure was the best for the high selectivity of adsorption g−1 after 200 cycles at 250 mA g−1, respectively (Fig. 20 c-d).198 of CO2 molecules from the CO2 and hydrogen mixture. Although HNMC material prepared from honey showed a superior nanoporous carbons with slit, foam like and random porous performance towards Li ion battery with a reversible capacity of structure showed the adsorption but the selectivity was much 1359 mAh g−1 after 10 cycles at 100 mA g−1 and excellent rate inferior to that of porous carbon with tube like structures.268 capability and cycling stability of 722 mAh g−1 after 200 cycles at 1 A g−1 (Fig. 20 a-b). The same material demonstrated the initial 6.5 Nanoporous carbon for batteries discharge and charge capacities of 977 and 427 mAh g−1, Modified nanoporous carbon materials have been extensively respectively for Na ion battery.58 utilized as electrode materials in the Lithium ion and post Li-ion Liang et al. have investigated the performance of batteries such as Li-S, Na-ion and Na-S batteries owing to their mesoporous nanocomposite by using N-OMC/SiO2 as an anode superior textural properties together with high conductivity and material for lithium-ion batteries. The initial discharge and stability. Duan et al. reported on the usage of Sn nanoparticles charge capacities of the N-OMC/SiO2 nanocomposite electrode incorporated mesoporous carbon as an anode material for Li- were measured to be as high as 3900 and 1996 mAh g−1, ion battery.178 The charge/discharge voltage curves observed respectively, with a Coulombic efficiency of 51%. The discharge for nano-Sn/mesoporous carbon showed a typical sloping capacity retained a large value of 740 mAh g−1 after 50 cycles, voltage profile associated with lithium alloying-dealloying with which was about two times higher than the theoretical value of 93 nano-sized Sn in the sample. The initial columbic efficiency was graphite. TiO2 supported on nitrogen-doped carbon foams 60%, which was calculated according to the discharge capacity (NCFs) were also used as a free-standing and flexible electrode of 1246 mAh g−1 and charge capacity of 747 mAh g−1. The for lithium-ion batteries (LIBs). When TiO2-NCF was directly columbic efficiency increases to 85% during the 2nd cycle, 90% used as a flexible electrode in a LIB, a capacity of 188 mAh g−1 to the 3rd cycle, and 97% above after 7 cycles. Urchin-like was achieved at a current density of 200 mA g−1 under a

Fe3O4@C-N composites displayed an excellent electrochemical potential window of 1.0–3.0 V, and a specific capacity of 149 mA performance with a reversible specific capacity of 800 mAh g−1 h g−1 after 100 cycles at a current density of 1000 mA g−1 is after 100 cycles at 500 mAh g−1 in the 0.01–3 V voltage range at maintained.269 The addition of sulphur into the NOMCs can help room temperature.194 This significant electrochemical these nanostructures to be used in Li-S battery applications. Qu

performance of urchin-like Fe3O4@C-N composites was et al. reported on the preparation of sulfur–HNMC composite attributed to the unique urchin-like structure and the N-doped with 53.3 wt% sulphur by a melt-diffusion method for high rate mesoporous carbon shell. capability and long cycling stability cathode materials in Li-S battery.270 The S–HNMC composite cathode exhibited a high

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ARTICLE Journal Name initial discharge capacity of 1209 mAh g−1 and retained as high 6.6 Nanoporous carbon for carbon capture and storage −1 as 600 mAh g after 200 cycles at 1 C. Chen et al. reported on Global warming leading to drastic climatic changes happening the usage of NM-CMK-3/S composite with 50 t% of Sulfur in the due to the increasing concentration of carbon dioxide in the Li-S battery, which shows the high initial capacity of ca. 950 mAh atmosphere added through various anthropogenic sources is −1 g , 100% Coulombic efficiency, and excellent cyclic stability of inevitably one of the major environment crises of our times.272, −1 about capacity retention ratio of 80% (750 mAh g ) after 100 273 There is an urgent need of developing materials and cycles with a decay of only 0.2% per cycle.139 The high technologies to combat the dangerous emissions of CO2 from performance was attributed to the presence of microporsity industrial sectors such as power generation plants, cement and nitrogen contents which provided synergetic effects. These production, petrochemical production, aluminium, steel and results explained the importance of having nitrogen on the plastic manufacturing industries etc. Carbon based materials surface of the carbon walls for energy storage applications. especially, ordered mesoporous carbon-based adsorbent with Balach et al. described the high initial discharge capacity of highly developed textural parameters are regarded as a 1364 mAh g−1 at 0.2C for NOMC/S composite with 50wt% of potential solution to tackle the problem of industrial CO2 sulfur. The composite material also showed extremely high emission. Two key parameters required for efficient CO2 −1 cycling stability with a high reversible capacity of 566 mAh g capture by an adsorbent include high specific surface area and and a negligible degradation rate of 0.037% after 1200 cycles at the presence of nitrogen containing functional groups on the 145 0.5 C. Liu et al. demonstrated that the S/CPAN-800 composite surface of carbon.274 Several reports can be found in the was an excellent material for Li-S cells, which has delivered a literature for increasing surface area of different kinds of −1 high initial discharge capacity of 1585 mAh g and enhanced carbons using chemical activation.275, 276 However, this −1 capacity retention of 862 mAh g at 0.1 C after 100 cycles and procedure might not be suitable for ordered carbons as it may high Coulombic efficiency of around 100%. These results greatly result in deformation of the order and affect the properties of outperformed the S/CMK-3 composite cell without nitrogen the carbon. A few ordered mesoporous carbons are discussed

below to ascertain the role they can play in capturing CO2. Wang et al. synthesized ordered mesoporous carbon CMK- 3 through hard templating procedure using SBA-15 as a 277 template for CO2 capture. They reported a surface are of 1115 m2 g−1 and pore volume of 1.11 cm3 g−1 and the material -1 adsorbed 42 mmolg of CO2 under high-pressure conditions (36 bar). It is to be noted this much high CO2 uptake was observed using CMK-3 preabsorbed with water that decreased to 18.5 mmolg-1 with dry CMK-3. The heat of adsorption was observed to 55 kJmol-1, which indicates strong physisorption between

CMK-3 and CO2. As previously discussed, the textural properties of the OMCs were significantly improved after the activation with KOH. Especially, the quantity of the micropores can be significantly enhanced after the activation. Bao et al. reported that the presence of ultra micropores of size <0.5 nm is a critical factor

for enhancing the CO2 adsorption and CO2/N2 selectivity of the nitrogen doped hierarchical carbon derived from polypyrrole.278

They compared the CO2 adsorption statistics for N-doped carbons made at 500°C and 800°C and even though the latter had a significantly high surface area, it still showed a relatively

lesser amount of CO2 adsorption, which defies the common theory that high surface area, leads to high CO2 adsorption. Eventually, a low temperature carbonization to protect the ultra micropores widening and retaining of nitrogen containing functional groups was concluded as to be the most critical doping, which maintained only 400 mAh g−1 capacity at 0.1 C parameters for high CO2 adsorption. after 100 cycles.271 The enhanced performance was attributed to the nitrogen doping combined with sulphur, which 6.7 Electrocatalysis significantly improved the wettability of electrolyte and the Hetero-atom and non-precious foreign element doped carbon conductivity of the electrode. These results reveal the nanomaterials are considered as the low cost and highly importance of doping of dual heteroatoms in the carbon efficient electrocatalysts alternative to the commercial framework structure of NOMCs. platinum (Pt) based electrocatalysts. Among the doped carbon nanomaterials, nanoporous carbon materials modified with B,

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N, S, P and non-precious elements are more attractive sharply increased peak current towards the ORR. The apparent electrocatalysts for the oxygen reduction reaction (ORR), number of electrons involved in ORR for NOMC-800 prepared hydrogen evolution reaction (HER) and oxygen evolution at 800 C is close to 4-electron, according to Koutecky–Levich reaction (OER). In this section, we will summarize the role of equation. This indicates that the oxygen reduction follows structure, morphology and the single or dual heteroatom mainly the four-electron pathway either by reducing oxygen doping in the OMCs affecting the final electrocatalytic directly to OH− ions or by reducing it to hydrogen peroxide performance of these materials. which is subsequently further reduced to OH− ions.57, 98, 161 NOMCs synthesized via a facile dual soft-templating 6.7.1 Oxygen reduction reaction (ORR) procedure showed the most positive onset potential (–0.11 V) and the highest reaction current density at a certain overpotential, suggesting the fastest reaction kinetics via close to four electron reaction pathway with higher limiting current density.90, 99, 101 NOMC materials prepared from pyrrole or aminopyridine and Fe catalyst outperformed the Pt counterpart and the performance was significantly improved by increasing the pyrolysis temperature from 800 to 1000 °C.67, 281 Nitrogen- doped mesoporous carbon nanosheets (NMCNs) fabricated from the thermal treatment of polyaniline enwrapped cobalt

hydroxide (Co(OH)2) nanosheets followed by the subsequent acid etching manifested an excellent ORR performance with the onset potential of –0.119 V, the half-wave potential of –0.182 V and the limiting current density of 5.06 mA cm–2. These values were comparable to the commercial Pt/C (–0.164 V and 5 mA cm–2).282 A nitrogen-doped mesoporous carbon containing a network of carbon nanotubes (CNTs) also showed an excellent ORR ORR is a key process in the fuel cells (FCs) for generating activity, with 59 mV more positive onset potential and 30 mV electricity by electrochemical reduction of oxygen and oxidation more positive half-wave potential than a Pt/C catalyst, and also of hydrogen by production of water as the by-product. The most much longer durability and stronger tolerance to methanol suitable electrocatalyst for ORR is the platinum (Pt) based crossover than a Pt/C catalyst.283 Highly ordered N-doped electrodes. However, the scarcity and the high cost of Pt are the mesoporous carbon/graphene frameworks (N-MCF/N-MGF) primary barriers to commercialize the Pt based electrocatalyst prepared by using super lattice of self-assembled Fe3O4 for fuel cells. Apart from the high cost, the Pt-based electrode nanoparticles as template showed a 47 mV positive shift in the also suffered from the susceptibility to fuel crossover and CO half-wave potential and higher current densities compared with poisoning under electrochemical conditions. Therefore, the Pt/C (2.24 and 0.74 mA cm−2), demonstrating its superior numerous efforts have been devoted in seeking alternative ORR activity compared with the commercial Pt/C catalyst.284 non-platinum ORR electrocatalysts for FCs with a low cost and a Park et al. showed the ORR catalytic activity of NOMC high ORR activity. In this part, we review the latest advances on materials, which demonstrated the high selectivity toward H2O2 the fabrication of electrocatalysts based on the doped and over 90%. At 0.1 V, NOMC exhibited a ring current of 0.148 mA, Figure 21 (A) ORR results in 1M HClO4 for the prepared catalysts, (1) NDC, (2) BNDC, (3) PNDC, (4) BPNDC, and (5) Pt/C (40 wt %). (B) Calculated mass activities which corresponds to H2O2 formation at a rate of 3.06 pmol at 0.6 V (vs RHE) for the prepared catalysts and other N-doped carbon catalysts. −1 62 (C) RDE polarization curves of Fe−N−GC materials prepared at different s . Chen et al. also observed a well-defined oxygen reduction carbonization temperatures and Pt/C. (D) RDE voltammograms of FeNCSs and Pt/C at 1600 rpm. Reproduced with permission from ref. 279 and 182. Copyright peak at 0.68 V (vs RHE) in CV curve under O2 saturated 0.1 M 2012 and 2014, American Chemical Society. KOH solution for NHPCM prepared by using N-doped hierarchical porous silica monolith template and furfuryl alcohol functionalized nanoporous carbon materials. Choi et al. as the carbon source. The number of electrons involved in ORR demonstrated that the additional doping of B and/or P in the for NHPCM is in the range of 3.7 to 3.9 indicating that an nitrogen doped nanoporous carbon can enhance the intrinsic four-electron pathway is the dominant mechanism. No asymmetry of atomic spin density and improved the ORR significant change was observed in the ORR current density of catalytic activity.279 The ORR activity of the B, N-doped and P, N- NHPCM electrode after MeOH was added into the doped nanoporous carbon showed 1.2 and 2.1 times higher electrochemical cell, suggesting that it has remarkable than N-doped nanoporous carbons at 0.6 V (vs RHE) in acidic improved ability to avoid the crossover effects.65 media. The nanoporous nitrogen doped carbon catalyst Sulfur doped OMCs such as OMC-S-1, OMC-S-2 and OMC-S- incorporated with both of the B and P (BPNDC) depicted the 3 having sulphur contents in the range of 1.4 to 1.5 Wt.% best ORR activity of 2.3 times higher than NDC at 0.6 V (vs RHE), exhibited higher currents of 238.0, 282.3 and 376.4 µA, during which records –6.0 mA/mg of mass activity (Fig. 21 a-b).279, 280 the ORR, which are higher than that of unmodified OMC NOMC prepared from honey and glucose/ammonia precursors electrode. The number of electrons calculated to be for ORR on exhibited a significantly lower potential at −0.23 V as well as a OMC-S-3 were 3.3, 3.4, 3.5, 3.6 and 3.8 at different potentials,

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ARTICLE Journal Name which indicates that OMC-S-3 typically provides a four-electron activity and specific activity of 564 mA mg-1 Pt and 834 mA cm-2 transfer pathway for ORR.113 Yang et al. observed ORR peak at Pt, respectively, which may have been due to the presence of −0.19 V for P doped well-ordered mesoporous carbon (POMC), an appropriate amount of N atoms doped into the nanoporous which confirmed the excellent electrocatalytic activity of POMC carbon matrix.177 Pt nanoparticles on N-doped ordered for oxygen reduction. mesoporous carbon−Co composites (Pt/Co-N-OMC) displayed POMC also exhibited high catalytic activity for ORR with an extraordinary selectivity for oxygen to evade crossover effects of the methanol and thereby outperformed the commercial Pt/VC electrode. For the Pt/VC catalyst, a very strong peak at −0.18 and −0.21 V was observed for methanol oxidation in the CV curve, whereas the cathodic ORR peak vanished. In contrast, no noticeable change was observed in the oxygen-reduction current on POMC electrode.107, 285 Boron doped ordered mesoporous carbons (BOMCs) were also employed for ORR. These catalysts exhibited a substantial ORR cathodic peak at around −0.27 V. The maximum peak current density on BOMCs is −1.46 mA cm−2, whereas unmodified OMCs and Pt/C registered maximum peak current densities of −0.84 and −0.97 mA cm−2, respectively.103 BOMCs electrode showed the significant onset potential shift towards positive side to −0.16 V with the limiting diffusion current density at −0.80 V, which is about 1.7 times stronger than that of undoped OMCs catalysts. The number of electrons participated in the ORR for BOMCs electrode at −0.50 V was found to be 3.86 and increased to 4 at more negative potentials, indicating that oxygen reduction follows mainly the four-electron pathway either by reducing oxygen directly to OH− ions or by reducing it to peroxide which is subsequently further reduced to OH− ions. S and N dual doped ordered mesoporous carbon (SN-OMC) materials were also successfully employed for ORR applications. It was found that the dual doping helped to enhance the ORR electrocatalytic activity (−0.186 V) in alkaline media with desirable current density, methanol tolerance and long-term stability. The number of electrons involved for SN-OMC during the ORR ranges from 3.93 to 3.95, very close to 4.0, indicating that it favoured a four-electron ORR process.111, 112

The ORR onset-potential (1.01 V), E1/2 value (0.86 V), and current density (9.6 mA cm−2) of the Fe−N−GC electrode the mixed kinetic diffusion current between 0.48 to 0.75 V with prepared by heating 2,2-bipyridine and Fe chelates at 900 °C the highest onset potential at 0.72 V in oxygen saturated 0.5 −1 with 0.2 mg cm−2 loading were higher and larger than those of mol L H2SO4 electrolyte at a rotation rate of 1600 rpm and scan −1 ∼ the values obtained on commercial Pt/C-JM electrode with 20 rate of 5 mV s and it also exhibited the highest limiting current 287 2 and onset potential. µgPt cm loading and the previously reported NPMCs with 0.3−0.4 mg cm−2 loading in 0.1 M KOH solution. These results Hollow graphitic carbon spheres with Fe–N-doped indicated its superior catalytic activity in alkaline medium (Fig. mesoporous shells (FeNCSs) prepared via in situ polymerization 181, 182 exhibited very superior ORR activity with a half-wave potential 21 c-d). Ultra fine Fe2N nanocrystals incorporated in E mesoporous nitrogen doped graphitic carbon spheres ( 1/2) of 0.886 V in 0.1 M KOH, 15 mV more positive than that of commercial Pt/C catalysts.288 Liang et al. elucidated the four- (Fe2N/MNGCS) were also utilized for ORR applications. The catalysts demonstrated the half-wave potential of 0.881 V vs electron reduction performance of oxygen in 0.5 M H2SO4 at RHE, high selectivity towards 4e- oxygen reduction process, room temperature by using cobalt−nitrogen-doped (C−N−Co) excellent long-term stability with 95.2% of the initial current and iron−nitrogen-doped nanoporous carbon (C−N−Fe), retention after 60,000 s of continuous operation and good prepared from vitamin B12 (VB12) and the polyaniline-Fe (PANI- tolerance against methanol crossover effect (94.9% of the Fe) complex. Among all of the catalysts, C−N−Co fabricated from current remained prior to 4.0 M methanol injection in alkaline VB12 and silica nanoparticles exhibited a remarkable ORR media. This performance was much superior to that of the activity with a half-wave potential of 0.79 V, which is only 58 286 mV deviation from Pt/C and further demonstrated a high commercial Pt/C catalyst. Pt nanoparticles supported on ∼ selectivity of four electron, and excellent electrochemical nitrogen-doped porous carbon microspheres (Pt/CN) 180 demonstrated ultrahigh ORR activity at a pH of 8.4 with a mass stability up to 10000 cycles.

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Mesoporous Fe10@NOMC catalyst prepared from reviewed. In 2015, Lin et al. successfully used N-doped ferrocene-based ionic liquid was also utilized for ORR. The mesoporous few-layer carbon with a large surface area of 1900 results showed that the catalyst exhibited a comparable onset m2 g−1for the supercapacitor applications. It was reported that potential and the half-wave potential (0 V vs. MMO) for the Pt/C the materials showed the highest ever specific capacitance of −1 −1 −3 and close values to the Fe/Fe3C-melamine/N-KB composite but 810 F g and 710 F g and volumetric capacity of 560 F cm −1 superior long-term stability to 20 wt% Pt/C in identical test and at 1 A g in 0.5 M H2SO4 and 2 M Li2SO4 electrolyte using conditions for ORR with four-electron transfer pathway under an Ag/AgCl reference electrode and a Pt counter electrode.56 alkaline conditions. Fe10@NOMC catalyst showed perfect ORR The electrochemical cell withstood the capacity for 50,000 selectivity in methanol containing electrolyte, whereas a cycles between 0 and 1.2 V. The device also demonstrated the significantly high methanol oxidation current is detected for the highest specific energy of 23.0 Wh kg−1 and a specific power 183 −1 Pt/C catalyst under the same conditions. Fe3O4 embedded density of 18.5 kW kg based on the device weight in 2 M Li2SO4 into nitrogen-doped mesoporous carbon spheres electrolyte. Electrochemical impedance spectroscopy showed

(Fe3O4/NMCS) with the iron content of 3.35 wt% was used as a that OMFLC-N has the lowest equivalent series resistance of robust catalyst for the ORR in alkaline media. It showed the ~0.8 ohms, better than that of OMFLC without N doping and excellent electrochemical performance in terms of more CMK-3 (Fig. 22). Wei et al. reported on the supercapacitor positive onset potential of 1.036 V vs RHE, half-wave potential device fabrication by using rich nitrogen-doped ordered of 0.861 V and much better methanol tolerance and long-term mesoporous carbon, which showed the specific capacitances of 289 −1 −1 durability, in comparison with that of 20% Pt/C. 262 F g (in H2SO4) and 227 F g (in KOH) at a current density −1 −1 −1 Three-dimensionally (3D) ordered mesoporous Fe-N/C of 0.2 A g and 244 F g (in H2SO4) and 213 F g (in KOH) at a fabricated from the soft templating approach manifested the current density of 0.5 A g−1, which are much better than that for high onset potential (1.018 V), half-wave potential (0.812 V) and the mesoporous carbon FDU-15 without any nitrogen content limited-diffusion current density (5.98 mA cm−2) in both acidic (110–130 F g−1).87 These results revealed that the coating of and alkaline electrolytes. The number of transferred electrons nitrogen doped carbon on the surface of the support was much (n) was calculated to be 4.08-4.20 between 0.40 and 0.60 V for more effective than the bulk NOMSs in the supercapacitor mesoporous Fe-N/C, confirming the dominant 4 e− oxygen applications. reduction mechanism.290 Cobalt-nitrogen-doped three- The nitrogen doped hierarchical porous carbon nets dimensionally (3D) ordered macro-/mesoporous carbons (Co-N- exhibited high specific capacitance of 537.3 F g−1 and 306.3 F -3 −1 OMMCs) prepared from dual-templating synthesis approach cm at 0.5 A g current density in a 0.5 M H2SO4 electrolyte. exhibited a highly positive ORR half-wave potential of 0.83 V The material also presented an outstanding cycling stability vs. RHE, which is only 0.01 V deviation from the Pt/C catalyst with 98.8% retention of their initial capacitance after 10000 ∼ ( 0.84 V vs. RHE). The catalysts also provided a higher diffusion- cycles at 5 A g−1.164 NOMC prepared from phenol–urea– ∼ limited current density than commercial Pt/C, indicating a large formaldehyde exhibits specific capacitance of 225 F g−1 at a ∼ quantity of exposed active sites on the Co-N-OMMC. The current density of 0.5 A g−1 and it is showed good number electrons involved in the ORR for Co-N-OMMC was electrochemical stability even after 1000 cycles at current calculated to be 3.9 at 0.5 V vs. RHE, revealing that the Co-N- density of 5.0 A g−1.92 - OMMC favoured a 4e oxygen reduction process and O2 was Microporosity has been introduced in the NOMCs via reduced to OH−, which is same with Pt/C catalyst. The activation and other techniques to enhance the specific chronoamperogram of the Co-N-OMMC showed negligible capacitance of the materials. Liu et al. reported on the performance attenuation even after 25 h of continuous enhanced supercapacitor performance of activated NOMC operation at 0.5 V vs. RHE, in contrast to a sharp activity loss of electrode material with the mass loading of ~3 mg cm-2 yielded commercial Pt/C, demonstrating the high stability of Co-N- a high specific capacitance of 186 F g−1 at a current density of OMMC for ORR.187 0.25 A g−1 and a good capacitance retention of 75% at a high discharge current density of 20 A g−1 in ionic liquid electrolyte. 6.8 Nanoporous carbon for supercapacitance Increasing the mass loading to ~12mg cm-2 gave rise to only a −1 159 Supercapacitors, which are also known as electrochemical 10% capacitance decay at 20 A g . Almeida et al. capacitors, provide a high power density (>10 kW kg−1), fast demonstrated that the NMC-T material showed a specific −1 charge/discharge process (within seconds) and long cycling life capacitance of 190.2 F g and retained 73% of its capacitance −1 (>105 cycles).291, 292 Nanoporous carbon based materials are when the current density was increased from 0.5 to 8.0 A g . In considered as the attractive electrode materials for addition, the specific capacitance of NMC-T retained up to 98% supercapacitors owing to their extremely high specific surface of their stored charges or initial capacitance after 1,000 charge– −1 66 areas, large pore volumes and pore diameters, in combination discharge cycles at a current density of 2.0 A g . NOMCs with the simple synthesis processing, non-toxicity and high prepared via aqueous cooperative assembly route −1 chemical stability. There have been a quite number of review demonstrated a high specific capacitance of 186 F g at a −1 articles reported on this topic.291-293 Therefore, in this review, current density of 0.25 A g and a good capacitance retention −1 recent developments on the utilization of these nanostructures of 75% at a high discharge current density of 20 A g in ionic 159 for supercapacitor applications for the past five years are liquid electrolyte.

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Nitrogen-doped micro-mesoporous carbon material role in enhancing the electrochemical performance of the ZTCs. exhibited a reversible specific capacitance of 226.3 F g−1 at the For example, Kyotani et al. also reported on the large current density of 1.0 A g−1 in 6 M KOH electrolyte and 75.5% of pseudocapacitance (330 F g-1) of electrochemically oxygen its initial capacity can be retained after 2000 cyclic tests.137 A functionalized zeolite template carbon (ZTC) in organic maximum capacitance of 237 F g−1 is reached for the NOMC electrolyte.296 The formation of anion and cation radicals of prepared by using ionic liquid precursor at a current density of oxygen functionalities offers pseudocapacitance which is 0.1 A g−1. The specific energy of a cell made from two identical responsible for the enhancement of the total specific NOMC electrodes is more than 83 Wh kg−1 (unpackaged) for capacitance of the functionalized ZTC. These results provide a 1100 cycles at a current density of 1 A g−1, which is correspond clear evidence that the functionalization of the ZTC is one of the to a specific energy of 25 Wh kg−1 in a commercial-style, key elements and can be used for tuning the electrochemical packaged device, which typically contains 30 wt% active performance of ZTC. material.81 Linnemann et al. demonstrated on the simplifying of the Hierarchical mesoporous carbons with different boron supercapacitor electrode fabrication process through the contents (from 0.42 to 2.37 wt.%) showed a specific capacitance electrodeposition of the carbonized metal organic framework −1 297 of 180 F g in H2SO4 aqueous solution at a current density of 1 (MOF) based films on the current collector. The MOF films are A g−1.106 Sun et al. described an advanced supercapacitor well attached to the metal substrate during the carbonization material based on nitrogen doped porous graphitic carbon process under argon atmosphere forming highly

(NPGC), which showed an excellent capacitive behaviour with electrochemically active Co3O4/C and Mn3O4/C hybrid specific capacitance of 293 F g−1 at a current density of 1 A g−1, materials. At the 50th cycle, the integral capacitance of the −1 long-term cycling stability at about 5000 cycles, and high Mn3O4/C bilayered system was 160 F g referring to Mn, 116 F 96 −1 −1 coulombic efficiency in KOH electrolyte. Tang et al. g referring to Mn3O4 and 102 F g referring to MnO2 at the implemented supercapacitor device by using NHPC-3D having scan rate of 20 mV s−1. This value is superior to the 298 8.2 wt.% of nitrogen functionalities as the active electrode Mn3O4/graphene material reported by Lee et al. material, that exhibits a specific capacitance as high as 252 F g−1 Fransaer et al. reported on the preparation of mesoporous at a current density of 2 A g−1. The device also shows high layered Ni-Co mixed metal oxides-carbon composite electrodes capacitance retention of 75.7% with specific capacitance of 190 on the Ni foam by using Ni-Co mixed metal-organic frameworks F g−1 at a higher current density of 20 A g−1.73 A NOMC material (MOFs) with the above mentioned method.299 This electrode demonstrated a reversible specific capacitance of 308 F g−1 at a exhibited a high capacitance of 2098 mF cm−2 and superior rate −1 −2 current density of 0.2 A g in aqueous H2SO4 electrolyte with performance of 93% from 1 to 20 mA cm at a current density 58% capacity retention of 131 F g−1 at a current density of 20 A of 1 mA cm−2. These are the best methods for the fabrication of g−1.97 Song et al. depicted that the NMMC electrode has the high efficient supercapapacitor electrodes using MOF derived specific capacitance of 325 F g−1 at current density of 0.2 A g−1 carbons which does not require any additional processing steps 76 in aqueous H2SO4 electrolyte. Xu et al. demonstrated that a or templates. microsphere-like nitrogen-doped mesoporous carbon/nickel- N- and O functional groups containing nanoporous carbons cobalt layered double hydroxide (NMC/NiCo-LDHs-M) derived from zeolite template showed a large pseudo- −1 −1 composite displayed a high specific capacitance of 272.6 F g at capacitance of 312.4 F g in H2SO4 electrolyte and it can −1 1 A g and outstanding electrochemical capacitance retention operate at 1.2 V in H2SO4 with a good durability beyond 4000 of 87.2% of initial capacitance even after 10,000 cycles.101 cycles.300 Wang et al. demonstrated that the NOMC materials OMCs derived from zeolite based templates have been can have the specific capacitances of 76 F g−1 and 21 F g−1, employed as electrodes for supercapacitor applications owing respectively, at a current density of 0.1 A g−1, which was to their better specific surface area and small pores. Kyotani et measured by galvanic charge and discharge process.86 The al. studied supercapacitance performance of zeolite templated diffusive resistances (RD) of NOMC electrodes are of 0.7 and 1.3 B and N doped ordered microporous carbon (N-ZTC) materials ohm, respectively. The specific capacitance of nitrogen and by using zeolite Y as a template. Among the materials prepared, sulphur doped ordered mesoporous carbon (NSOMC) reached N-ZTC demonstrated with a high capacitance of 180 F g-1 in 1 M 180 F g−1 in KOH aqueous solution at a current density of 1 A g−1, 294 TEABF4/PC electrolyte. Amoros et al. reported on the with approximately 39.5% enhancement over CMK-3, despite fabrication of thin films of zeolite-templated carbon (ZTC) on a the specific surface areas of NSOMC is only about 70% of the carbon current collector by the combination of chemical and CMK-3.110 NOMC material with a nitrogen content of 6.7 wt% 295 −1 electrochemical synthesis protocols. FAU nanozeolites were showed a high capacitance of 264 F g in 1.0 M H2SO4 deposited by an electrophoretic deposition (EPD) technique electrolyte at a current density of 0.5 A g−1 and a good rate from colloidal suspensions on porous carbon discs. Binderless capability with a capacitance retention of 226 F g−1 at 10 A g−1. continuous thin films of ZTC were materialized by subjecting the The NOMC electrode also delivered an excellent cycling stability resulting composites to chemical vapour deposition (CVD) of without capacitance fading over 10000 cycles.59 Ling et al. acetylene gas followed by HF washing. The prepared thin ZTC demonstrated that NOMC prepared by using PDA precursor layers show area capacitance values over 12 mF cm-2, which is exhibited a high specific capacitance of 538 F g−1 at a sweep rate one of the best value for electrodes in microcapacitors. The of 5 mV s−1. NOMC material delivered a large capacitance of 186 functional groups on these microporous carbons play a huge F g−1 at a high current density of 3 A g−1. The NONC

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supercapacitor electrode remained more than 93% of the initial formed a very effective CD-aptamer complex which provided a capacitance even after 5000 cycles, exhibiting excellent cycling very fast and sensitive fluorescent detection of Salmonella stability.60 A graphitic ordered mesoporous carbon (G-OMC) typhimurium. The limit of bacterial detection was 50CFUml-1 prepared from DA and NiO template showed the specific while a linear relation was found between concentration of capacitance of 183 F g−1 and 68 µF cm−2 at current density of 0.1 bacterium and fluorescence intensity in the range of 103 to A g−1.61 Although the N and NiO functionalities were there in the 105CFUml-1. This conjugated probe was also tested for real samples, they registered poor specific capacitance which might samples of eggshell and tap water and the results were very be attributed to the low specific surface area of the prepared similar to conventional plate count method which suggests the samples. potential application of these systems for detection of Nitrogen- and sulfur-codoped 3D cubic ordered mesoporous salmonella typhimurium in real situations.302 carbon (KNOMC) with controlled dopant content (10.0−4.6% for Simultaneous detection of Vibrio parahaemolyticus and nitrogen and 0.94−0.75% for sulfur) demonstrated the specific Salmonella typhimurium was also possible using a combination capacitance of 320 F g−1 at a current density of 1 A g−1 in 2M of green (gQD) and red quantum (rQD) dots with carbon aqueous KOH electrolyte. However, the specific capacitance nanoparticles. With the attachment of a specific aptamer, the decreased quickly during the first 10 cycles, but the specific respective QD’s-CNP assembly was able to measure the FRET capacitance retained almost 100.0% during the 20−1000th fluorescent changes from interaction of target bacteria within a cycles. After 1000 cycles, the specific capacitance reached to linear range of 50 to 106CFUml-1 and detection of limit as 25 and 247 F g−1.301 NOMCs with a high surface area of 1741 m2 g−1 and 35CFUml-1 for each bacterium respectively. The detection nitrogen content up to 15 wt.% exhibited a specific capacitance capability of the sensor platform using plate count method of 230 F g−1 at a current density of 0.5 A g−1 and good rate showed consistency when compared to shrimp and chicken as capability of 175 F g−1 at 20 A g−1 with capacitance retention of real solid samples for analysis.303 77.4% in 6 M KOH aqueous electrolyte.78 These results revealed An GQDs–AuNPs FRET biosensor was developed for S. that the optimum amount of N and S together with the excellent aureus specific gene sequence detection by immobilising surface area and structural order is the key to obtain high capture probe on GQD and conjugation of reporter probes on specific capacitance for the samples. AuNPs. Then, the hybridization of target S. aureus oligos within Nitrogen and phosphorus dual doped ordered mesoporous a conc. range of 100nM to 400nM packed between the GQD and carbon (NPOMC) demonstrated a high specific capacitance of AuNP layers formed a sandwich structure which triggered 220 F g−1 at a current density of 1 A g−1, a good rate capability of fluorescence resonance energy transfer (FRET) effect. One of 178 F g−1 at 16 A g−1 with capacitance retention of 81% and an the interesting features of this work was that the detection limit excellent cycling stability of 91% in 6 M KOH aqueous of this biosensor was 1nM for S. Aureus specific gene detection, electrolyte.171 This value was lower than the N and S doped or which clearly demonstrated the good selectivity. In a single and N and O doped NOMCs. Hierarchically nitrogen doped ordered double mismatched oligos system at 200nM, the sensor mesoporous carbons (HNMC) synthesized from polyhedral recorded a quencher efficiency of 93% for target oligos and 22- oligosilsesquioxanes (POSS) demonstrated a nearly ideal 37% for mismatched oligos which indicated the specificity of the rectangular shape CV in a wide voltage window from −2 to 2 V. sensor. This simple technology could be used for the whole These HNMC materials showed a gravimetric and volumetric genome of S.Aureus detection which would open the platform specific capacitance of 163 F g−1 and 106 F cm−3 at a current for the detection of foodborne pathogens. This would density of 0.25 A g−1 in ionic liquid electrolyte and also showed significantly support the food safety and environmental the slow capacitance decay with increase of discharge rates, in screening.304 particular, at 20 A g−1. It also showed a high capacity of 141 F g−1 with 89% capacitance retention.162 Binder free supercapacitor electrodes based on nitrogen-doped mesoporous carbon 7. Conclusion and future prospects −1 microfibers (NMCMFs) exhibited specific capacity of 189 F g at Despite the fact that tremendous amount of progress has been −1 −1 a scan rate of 5 mV s , excellent rate capability of 107 F g at made in the fabrication of nanoporous carbons with −1 100 mV s and durability (maintained over 96% of the initial contemporary structures and unique morphologies, exciting capacitance after 10000 cycles) in 6 M KOH aqueous opportunities have still persisted for their functionalization in 163 electrolyte. All these results revealed that optimized doping developing multifunctional properties for divergent specific and the structural control of OMCs are the key to fabricate the applications. The integration of different heteroatoms into the best electrode system for the energy storage application. nanoporous carbon framework together provided us a new Ultimately, this information could be used for the design of the class of materials exhibiting many unmatched properties. By best energy storage system with a considerable cost reduction controlling both chemistry and geometry of these by adopting necessary low-cost modification of OMCs. functionalized hybrid nanoporous carbon based materials using different templates or micelles, these functional materials have 6.9 Carbon nanomaterials based pathogen sensors already had applications in wide variety of different Carboxyl modified carbon dots prepared by hydrothermal technological and scientific fields. Various strategies have been carbonization of citric acid combined with amine based aptamer applied for the fabrication of nanoporous carbon materials with exemplary textural parameters starting from the basic synthesis

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ARTICLE Journal Name methods, such as templating techniques to the advanced possibilities for the synthesis of mesoporous carbons surfactant mediating approaches. overcoming the intrinsic limitations imposed by the hard In this review, we have reviewed and discussed the recent template method. significant breakthroughs on the synthesis, and structure, In this review, we have thoroughly conferred the recent morphology and functionalities control of ordered nanoporous research developments and trends in both hard templating and carbon materials. We have also shown that how the structures soft templating techniques for the synthesis of highly ordered and morphological control affect the final textural properties of nanoporous carbons without any dopants and also the materials and their roles on the final performance of the functionalized nanoporous carbons with mono, binary and materials in various applications including adsorption, carbon ternary hetero atoms doping and foreign elements. Hetero capture, energy storage batteries and supercapacitors, atom doping, functionalization and morphological control of electrocatalysis and heterogeneous catalysis were discussed in nanoporous carbon materials are highly depend on the detail. We have also imparted the exhaustive analysis in the processing conditions, which make the precise tailoring for structure-function correlation of functionalized nanoporous extremely high textural parameters such as specific surface carbon materials and considered their diverse preparation area, pore volume and pore diameter in nanoporous carbon methods including mono or binary and even ternary doping materials, which dictate their efficiency in many applications. methods by using different heteroatoms (B, N, O, S, and P) and From the last few decades, there have been tremendous foreign elements (Fe, Co, Ni and Cu) containing natural and amount of research and development activities devoted to the synthetic carbonaceous precursors, surface modifications and discovery of new materials and technology for energy functionalization with organic and inorganic molecules and generation, storage and conversion, owing to the development nanostructures. of alternative, economical and sustainable energy resources to With these developed robust and reliable doping, meet the ever growing global energy demand and functionalization and templating strategies, a broad range of environmental impact on the heavy dependence of traditional nanoporous functionalized carbon materials with pore cavity fossil fuel based energy resources, which poses serious sizes in the range of 2-50 nm and various dimensions (1D, 2D challenges to human health, energy security, and and 3D) can be readily and selectively fabricated for promising environmental protection. As presented in this review, the fuel advanced technological applications. The prepared cell technology offers a viable approach to generate electricity functionalized nanoporous carbon materials have been from the electrochemical reaction of hydrogen and oxygen by effectively used mainly in electrochemical energy conversion production of water as the by-product, and virtually no and storage devices fabrication technologies. Their involvement pollution. The slow ORR kinetics on the cathode side is a key in electrochemical energy storage applications, including Li-ion step to limit the energy conversion efficiency of a fuel cell and batteries, post Li-ion batteries including Li-S, Li-air and Na-ion requires a substantial amount of the catalyst. Traditionally, batteries, and supercapacitors were presented in detail. Recent platinum (Pt) has been regarded as the best ORR catalyst. discoveries on energy conversion applications such as However, Pt-based electrode suffers from multiple drawbacks electrochemical oxygen reduction reaction (ORR), hydrogen such as high cost, scarcity, and susceptibility to fuel crossover, evolution reaction (HER) and oxygen evolution reaction (OER) time-dependent drift and CO poisoning under electrochemical on functionalized nanoporous carbon materials were also conditions. Along with the intensive research efforts in reducing introduced in detail. By finely tuning the textural parameters, or replacing Pt-based electrode in fuel cells, heteroatom and morphology and doping concentrations of the nanoporous non-precious metal doped nanoporous carbon materials have carbon materials at different length scales, their performance in been discovered as a new class of electrocatalysts for ORR, adsorption, carbon capture, sensing, electrochemical energy which could dramatically reduce the cost and increase the storage and conversion performances can be significantly efficiency of fuel cells. The functionalized nanoporous carbon enhanced. materials successfully catalyze the O2 molecule via 4 electron Before inception of the block copolymer assisted soft reduction pathways at same or lower potentials than golden template synthesis method for the preparation of highly standard Pt based catalysts under both acidic and basic ordered mesoporous carbon materials, pre-prepared inorganic conditions. The nanoporous carbon materials also possessed porous materials mediated hard template nanocasting excellent long-term stability with almost retention of the initial approach was considered as the only method that can be used current even after several hours of continuous operation. They for the successful fabrication of mesoporous carbon with well- also showed a good tolerance against methanol crossover defined pores. The soft-template method relies on effect. The enhanced catalytic performance of the supramolecular micelle assemblies, which enhances the functionalized nanoporous carbon materials has been polymerization processes of carbon molecular precursors. The attributed to the electron-accepting/donating abilities of the soft templating method is thermodynamically driven, and heteroatoms or functional elements present in the nanoporous therefore depends on the chemical interactions between carbon framework, which create net charge on adjacent carbon supramolecular templates and carbon molecular precursors. atoms to facilitate the O2 adsorption and net charge transfer for Because of their facile synthesis and processing characteristics, ORR. soft templating synthesis processes governed by the block Another great opportunity for functionalized nanoporous copolymer templates have dominated and create new carbon materials lies in the efficient storage of energy

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generated by fuel cell technology, which is a win-win situation remarkable progress, their facile synthetic routes are still on its for these fascinating materials. The use of functionalized way of developments and the multiple heteroatom doping at nanoporous carbon materials has generated much excitement controllable places in nanoporous carbon frameworks. Further, in the field of energy storage systems, including process simplification is needed to lower the consumption of supercapacitors, Li-ion batteries and post Li-ion batteries. As it consumables and energy as well as decrease waste generation. was clearly explained in this review, the functionalized Moreover, the low yield of ordered nanoporous carbon nanoporous carbon architectures can be introduced with materials provided by current synthesis methods also remains heteroatoms, redox functional groups, functional elements, an issue from the perspective of their potential use in industrial metals, metal oxides, conducting polymers and alloys based processes. Irreversible acidic and basic moiety functionalization materials to enhance both electron and ion transport in the of nanoporous carbons with known and desired functional active materials for improvement of energy storage capability groups, it is possible to control anchoring of hetero atoms on and stability of the batteries and supercapacitor devices. Apart their surface in a desirable way. Surface functionalization of from the energy conversion and storage devices including, fuel nanoporous carbons also improve their solubility, stability and cells, batteries and supercapacitors, the future challenge is to reduce the agglomeration, which can help them with improved design and development of functionalized nanoporous carbon performance towards selective sensing of hazardous heavy materials having suitable band structure, with inbuilt functional metals, pathogens and toxins. It is quite surprising that recent moieties including organic or inorganic nanostructures in the days the interest towards the application of functionalised mesochannels electrodes. These electrodes should be able to nanoporous carbon for the drug delivery has been increasing, split the water molecules under electrochemical conditions for mainly due to the functionalisation methods that has the ability the facile production of hydrogen and oxygen which can be to enhance the compatibility of the nanoporous carbon connected to fuel cell technology that offers a viable approach materials. These methodologies allow the immobilisation of the to electricity generation directly from water without any DNA, protein, enzymes and drugs that can be finally involved in pollution. the in-vivo drug delivery. However, the practical applications of Although the functionalised nanoporous carbons offer these materials are still under investigation and very few studies excellent performances in the energy oriented applications, it is have offered as the proof of concepts. Therefore, a wide still needed to achieve the cost-effective way for their large- spectrum of research is deliberately needed for the biomedical scale production of cheap electrode materials and the applications. electrocatalysts which are both highly stable and reliable. These The research articles reviewed in this review article, are the major limitations for these exciting materials. Therefore, illustrate the fabrication of nanoporous carbons and their great the future challenge is to synthesize the highly pure interest towards their properties and applications. Carbons functionalized nanoporous carbon materials without any have already made a revolution in the world and the contamination in more economical way without using harsh nanoporous carbon materials are their fascinating parts and the conditions and expensive reagents but with a low-cost present trends in the ocean of carbon is the functionalisation of biodegradable carbon or nitrogen precursors. As discussed nanoporous carbon which is now making a history through above in this review, the functionalized nanoporous carbon small modifications and an outstanding improvement in the materials having high specific areas were found to be the best world. There is no doubt that a lot of opportunities are hidden

materials for CO2 adsorption. The future mega challenge for and the researchers should explore more on utilizing the materials scientists is to utilize both the in-built electronic and amazing potential of these functionalized ordered nanoporous absorption properties of the functionalized nanoporous carbons in the above suggested applications covering, energy,

carbons to convert the adsorbed CO2 into fuels and chemicals environment and health sectors. We are confident that the by using water as the hydrogen source through the information presented in this review would definitely support electrocatalysis. The proof-of-concept studies will certainly the advances in the research and development of ordered stimulate more research in the electrochemical reduction of nanoporous carbon materials.

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This review provides the recent progress and advances on the design, synthesis and high throughput applications of functionalized micro and mesoporous carbon materials.